It's not possible to migrate existing extensions between miniExtensions accounts.
1. Bought a subscription for the wrong account
If you have bought a subscription with an account different than the one you used for the free plan, the solution is to buy another subscription using your old account (the one you plan to keep), then ask us to cancel and refund your other account.
2. Change the account's owner
If you simply need to change the ownership of the account, you can just change the account's email address to something else.