Start first by check the fuses to be sure it has a good power supply. Next follow the wires up from the fuel tank. There will be a 2 wire plug ...1 wire is pink the other is pink and blue. Unplug it and put a small piece of wire in the guage end as a jumper. Put the dess on and see if it registers full. If it does the guage is good and the problem is in the fuel sender unit. If it doesn't work the guage is bad. If it does work, pull the baffle tube, and it could be the float in the tube that is bad, or gas logged. it might need replacing. Do this test and if it is in the baffle tube we can explain what to do from there. There are posts on the forum for your model, and I'll give you the correct link to follow the repair, for your exact doo.
Karl