Transmission Warning Messages and Park light flashing

Park light was flashing and about 12 hours later, I got a “Service Transmission Now - Unable to Shift Soon” message. I had no issues driving, transmission shifts smoothly. Tan codes and found that there was an “issue” with rear drivers side EPB Actuator. Replaced the actuator, but warnings never went away. Transmission message started becoming more frequent, starting at every 10 minutes, then every 2 minutes.
Checked battery, no issues, transmission fluid is fine, no codes in the TCM, just still a code in the brake system, C028F-04. Started the car and now it says, “Transmission Unable to Shift”.
Any advice on a fix for this? The internet has not been super helpful here, as I’ve seen a lot of these with different “fixes”. Is there a way to flash the system and see if it resets without a scan tool?