Changing time zone

Hi

As Im working as a sailor I often travel between time zones. But we are not always changing the time to fit the actual location. i.e. when sailing in the english channel we have UK time on one sinde and Euro time on the other.

On my phone and Ipad I normally can change the time zone manually but for some reason has it been set to automatic and the button is disabled.

Problem is that I use my Garmin watch as alarm clock this is getting the time signal from my phone. So passing the before mentioned english channel I will jump from one time zone to another without beeing able to do anything.

I can make my watch adjust time manually but it is very strange that Im not able to do the same on my phone og ipad.

Hope you can help