I put my iPhone inside water then the Face ID stopped working and there is a line on

Hello ~ Your iPhone has not been designed to be placed in water. Likely you will need it replaced.

About splash, water, and dust resistance of iPhone 7 and later - Apple Support

~Katana-San~

You damaged your iPhone and there is no way to fix it. You should NEVER put your iPhone in water. Liquid damage is permanent and often fatal. You need to buy a new iPhone now. If the phone still works at all, back it up, before its too late and you lose all your data. You'll be able to restore your data from backup when you buy your new iPhone.