You cannot change the currency for your Microsoft 365 subscription directly. The currency is tied to the country/region where your organization is headquartered. If you have moved to a new country and want to use a different currency, you will need to sign up for a new Microsoft 365 account in the desired country/region and purchase a new subscription there. This means you will have to cancel your existing UK account first.
It's important to note that changing your organization's country/region is not possible without creating a new account.
References: