I used to have an Iphone from work and my Apple watch was paired to it.
Now I bought a new Ihpone, gave back my old Iphone and I am unable to pair my apple watch to the new phone.
My Apple watch says: "wrong code, go to apple watch app and..."
There is no chance to enter the code manually.

But in the App I can only start to pair a new device, but the watch is still paired.

What steps do I have to do?

My Apple Watch is from series one and I don't know the software version nor how to determine it.