My iPhone fell inside water and the Face ID became disabled

Do you mean disabled? This document is specific to seeing a 'disabled' Face ID alert, and explains what to do when you see that notice. --> If an alert says Face ID has been disabled on your iPhone or iPad Pro - Apple Support

1. Check if there is an issue with Face ID in your iPhone's parts and service history. To do this, open the Settings app, tap General, then tap About.
2. If you still can't enroll your face or unlock your device with Face ID, you can take your device to an Apple Store or Apple Authorized Service Provider, or contact Apple Support about your iPhone or your iPad.

Judeofozor wrote:

so what do I do now?

If you still can't enroll your face or unlock your device with Face ID, you can take your device to an Apple Store or Apple Authorized Service Provider, or contact Apple Support about your iPhone or your iPad.

Did you follow the same advice to make an appointment at the Apple Store or take the phone to an authorized service shop?

You can find a list of authorized shops in your area by using the link just below:

This is a user to user support forum. People like yourself, happy to help others. ;-)

Liquid damage is not repairable.

Make an appointment at the Genius Bar of your local Apple Store or take it to your local authorized service provider.

The phone will have to be completely replaced.

Hello, where you able to fix the problem about your Face ID,I am asking because I have the same problem?