How do I get facial recognition to work with a third party screen

If your mention of a third party screen means that your phone has had a screen replacement with other than Apple screen, Face ID is unlikely to ever work. In most cases Apple can repair that which renders Face ID inoperable, but they likely will refuse you service since you have had non-Apple parts installed. But in case that is not what you mean, you can have the folks at Apple help you.

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You don’t. It will never function on that device again.

That phone is untouchable by Apple now that it’s been tampered with.

All that you can do is take the phone back to the shop and ask them to fix the phone. If they can't you will need a new phone.