Put a wipe on his belly before you take the nappy off and that will make him wee if he needs one. Or put a clean nappy under the dirty one, quickly wip off the dirty one and put on the clean one
Just gotta be quick lol! It does calm down after a while, when they're tiny babies they're constantly peeing. Especially when you change them and their bits get cold. I second using the doggo pads. We used them for months!! He's 7m now and doesn't do it very often now. If left unwrapped for too long and we do sometimes get accidents.
If you open the nappy, wipe something wet/cold or both just below his belly button it should trigger this reflex whilst still in his soiled nappy so you can change after and put him in a nice clean fresh one! xx
Before opening the diaper I wipe around his belly button with a wipe wait a few seconds and then open. That usually works for me because he lets out any pee he has when the cold wipe touches him