if i would like an apple tech to look at my phone to see why my face id doesn't work how much will it be

A diagnostic at an Apple Store is typically free. I've never paid for one. I'm not sure if there's a hardware problem with Face ID whether or not it can be individually repaired. I've heard of some iPhones where Face ID was repaired with a new front screen assembly.

And an Apple Authorized Service Provider, it's up to the business whether or not they charge a fee for a diagnostic service. I've heard of some that do charge and won't apply the diagnostic fee to any service.

No charge for inspection. You will be given an estimated cost of repairs.