I can’t connect my Apple Watch to my new IPhone 13 pro

See -> Set up your Apple Watch

Set up your Apple Watch – Apple Support (UK)

& please read again -> Related Article -> If you can't pair an Apple Watch with your iPhone

What model of phone is it and what version of ios is it running?

What model of watch is it and what version of WatchOS is it running?.

What troubleshooting steps have you tried?.

What errror messages are you receiving?.

Has this watch ever been paired to another phone?