I am not able to activate my Face ID

If your Face ID is not working, see this, If Face ID isn't working on your iPhone or iPad Pro - Apple Support and this If an alert says Face ID has been disabled on your iPhone or iPad Pro - Apple Support. If neither help, then use the Get Support link at the top of the page here to contact Apple Support for service, or make a Genius Bar appointment at your nearest Apple Store. 

What was the result when you followed the guidance in the Related Article above your name on this page, that you were reading just before you posted here? If the Related Article doesn't answer your question please post back with more details about the issue and another user in this user-to-user forum will try to help.