How do I replace the pressure control solenoid b?

On that CVT transmission the solenoids are an integral part of the valve body and are replaced with the entire assembly. However, that replacement isn't as simple as it sounds because of it being a CVT. You must have a dealer level scan tool and access to Nissans factory programming network before you start. Then you need to have a new valve body
with its configuration data as the replacement part, a used one won't work unless you can access the vehicle it is being removed from and can copy the configuration data from it as a working unit. This is because the data on each solenoid is slightly different and the TCM gets programmed with that data. The mechanical part is simple. Drain the pan of fluid, remove the pan and disconnect and remove the valve body and its harness, clean the surfaces and install the new part with a new filter and harness and follow the torque specs as shown. Refill the CVT with the correct fluid. The hard part is getting the new part and the programming. The part number is Nissan 3170529X0C. The new ones come with a memory stick or a CD with the data used during programming so that the TCM you have can control the solenoids. That data is as important as it being a new part because of the way the CVT wears and operates. You also want to look at the fluid as it comes out. If there is any metal in it it is best to replace the entire CVT.
These are the OE steps you have to follow for replacement of the control body. -

Connect CONSULT or equivalent scan tool
Select “CALIB DATA” in “TRANSMISSION”.
Select PRINT DATA (this is used for warranty service normally but includes info you will need later as well)
Write down the serial number (calibration file number) of the new control valve.
Compare the serial number (calibration file number) on the CD, QR code label and new control valve. All numbers MUST match.
Turn ignition switch ON.
Insert the supplied CD into CONSULT.
Select “Work Support” in “TRANSMISSION”.
Select “WRITE IP CHARA - REPLACEMENT AT/CVT”.
Select “OK” on the “Select IP characteristics data file” window.
Open the calibration file located on the supplied CD.
Confirm that the serial number (calibration file number) displayed on CONSULT screen matches the serial number (calibration file number) on the new control valve.
Select “Next” on the “WRITE IP CHARA - REPLACEMENT AT/CVT” Work Support screen.
Turn ignition switch ON, engine OFF.
Press the brake pedal.
Shift the selector lever to the R position.
Depress the throttle pedal half way and hold, then press “START” on the CONSULT screen.
Write data to the TCM according to the instructions on the CONSULT screen.
Select “End”.
Select “CALIB DATA” in “TRANSMISSION”.
Print page 1 of 7. (Again for warranty work normally)

Now you need to let the TCM learn the amount of wear in the CVT by relearning the characteristics of the unit as installed that is done using the scan tool

Step one -
Start the engine.
Select “Work Support” in “TRANSMISSION”.
Select “FWD CLUTCH POINT LEARNING”.
Perform learning according to the CONSULT display.

Next you perform the following process twice, once with cold fluid and once with it at operating temperature.

Set the parking brake.
Start the engine and wait 5 seconds.
Shift the selector lever to the N position and hold more than 2 seconds, then to D position and wait for transmission engagement.
Repeat step 3 ten (10) times.
Shift the selector lever to the N position and hold more than 2 seconds, then to R position and wait for transmission engagement.
Repeat step 5 ten (10) times.
Shift the selector lever to the P position and turn the ignition OFF.

Once you have completed those steps and you are sure it's operational you use the scan tool again to erase the fluid use table.

Select “WORK SUPPORT” in “TRANSMISSION”.
Select “CONFORM CVTF DETERIORTN”.
Touch “Clear”.
Then use the tool to clear any stored codes and take the vehicle for a test drive. The JATCO units they use are not the most robust and in most cases, if you have made it past 90-100K miles you normally replace the entire CVT with a new or reman unit from the dealership because they tend to have catastrophic failure not long after that mileage, it's also one of the reasons why the parts are not easy to get, 99% of the time they replace the CVT rather than try to repair it. The unit is then returned to the factory where it is rebuilt, and the cycle continues. The failure rates are why companies that tried out CVT transmissions from JATCO in their models dropped them soon after. Nissan and Mitsubishi continue to use them because they own JATCO.