With Face ID on the iPhone you will have to have the original Face ID components from your original display. It is not uncommon for some repair shops to damage these components when they are transferring them to the new display as they are fairly easy to damage if you are not being careful.
So if they didn’t transfer the original Face ID components from your display, or if they were damaged when it was replaced then it won’t be possible to get Face ID back on your phone to my knowledge. This is because those parts are paired to your logic board on the phone, the only way to get it back would be potentially repairing the original Face ID components and there are not many places that would be able to do this.