Hello, all licenses are managed by a third party and I do not have full control on the process.
As far as I know the only way to change account billing details is to create a new account then transfer the license to this new account.
Please create a new account on Freemius (here: https://dashboard.freemius.com/register/) then send me a new request using the old user email (so I know that they are really you), the license number and the new account email address.
