Unable to unlock Apple Watch SE with iPhone

Furious that this is so confusing. My iwatch doesn't have a series number just says iwatchSE 10.5 so I can't get the exact explanation on how to fix a problem. I've a locked watch and cannot unlock it with my iphone. The manual is inadequate because it falls short on all fixes. Failure to anticipate multi scenarios is a futile time waste. My timeline was transferred all my info to new phone paired my iwatch got my apps iwatch is locked. Now what?

[Re-Titled by Moderator]