Not sure this will work in your situation, but you can try disabling the account, then put their email address in the URL below and go to it with a global admin account. This should let you view and transfer all the forms on the account.
https://forms.office.com/Pages/delegatepage.aspx?originalowner=[email address]
https://learn.microsoft.com/en-us/microsoft-forms/admin-information#form-ownership-transfer
It does sound like the form may already have been transferred to another account though.