Release button on back of watch won’t push in
On the back of my watch, the release button won’t push in and I can’t change band
Apple Watch Series 3, watchOS 8
Don't force it. You might try cleaning it:
How to clean your Apple Watch - Apple Support
If that doesn't help, your best option may be to make an appointment at the Genius Bar in an Apple Store near you and let them look at it:
Genius Bar Reservation and Apple Support Options - Apple