Change phone/ watch to another provider

Here are the Apple Watch carriers : Apple Watch - Carriers - Apple

If the carrier supports Watch in your country or region, find a carrier-owned shop if that’s not who you were already visiting, or directly contact carrier support and ask.

fieryjack wrote:

3 don't support the cellular apple watch,only O2,EE and Vodaphone.

3 does support Apple Watch in some locations; in at least Denmark, and Hong Kong.

But yes, by the phrasing and by O2, I’d guess UK here, where 3 does not (yet?).

3 don't support the cellular apple watch,only O2,EE and Vodaphone.

If the op is with O2 then he is in the UK.