Apple Watch to get my cellular working

Hi I have a Apple Watch 3 series and the cellular has not been activated.( purchased from Apple store.

i spoke to EE today And requested to activate free date inc with purchase.

ee have said fine but I will need to factory reset my Apple Watch and re pair with phone and it will work.

do I really have to factory reset watch.

I am a little scared I won’t get it back up and running again if I do this ( but EE have said because it did not happen when I first set up watch this is the way to go.

has anyone else done this before

thank