The only option is to open a new account when you are in the new country and applying again like a new user. Prior to that, to comply with adsense guidelines, you need to close your old account (else you would have two accounts at the same time.
These are their rules - ofc you don't have to play by them if you don't want, there are always other ways...
If you receive bank payments from your old account, keep the bankaccount and everything running as is. Open a new account once you are in the new country. Apply for adsense. When approved, create new ad-units and place them on your previous websites. Then contact adsense to close your old account.
Or just keep both accounts. There is a lot of information on how to securely keep plenty of accounts alive at the same time.