Q: Changing my location from Germany to the uk

Hi no ice!

You're right, in order to use any payment method from the UK you need to refer to the article Change your iTunes Store country or region - Apple Support

in order for you to change the current location setup for your account, then you will be prompted to verify or provide your current payment method based on the location that you selected, make sure you have your new card info ready to use it before making the changes

 Hope it helps!