The answer to 'how to fix GFCI outlet' is to reset the GFCI outlet if it has tripped. GFCI (ground fault circuit interrupter) outlets are designed to trip and cut power when they detect a ground fault, which helps prevent electric shocks and fires. To reset a GFCI outlet, simply press the 'reset' button on the outlet. If the GFCI keeps tripping, there may be an issue with the wiring or the outlet itself that needs to be addressed.
If resetting the GFCI doesn't work or you're not comfortable troubleshooting the issue, it's best to call a licensed electrician to inspect and repair the GFCI outlet. Attempting to fix a GFCI outlet yourself can be dangerous if you're not familiar with electrical work.