Can not find the circuit breaker without power
If your GFCI is trying to reset then you do have power at the source conductor attached to you GFCI.

You need to remove the cover of the GFCI and carefully unscrew and pull out the receptacle. Use a non contact tester to see if there is power at the GFCI. If it does then get a helper and have them test the receptacle while you go through panel turn each breaker on then off until you find the one that turns the power off at the receptacle.