The flasher is up inside the dash, above the regular fuses. You will need to remove the lower dash panel to gain access to the flasher.
Remove the lower dash panel and use a flashlight to locate the flasher unit. Check the relay that you have identified by feeling the outside of the casing and turning on the turn signals. You should feel a mechanical clicking inside the flasher if you have chosen the right one.
Replace the bad flasher with the new one. Reinstall the lower dash panel and start the Grand Cherokee. Turn on the turn signals and check to see that the lights work as they should.