I can guide you in changing the Master Administrator of your QuickBooks Online (QBO) account.
To transfer Master Administrator role to an existing Company Administrator:
Click the Gear icon.
Select Manage Users.
Click the drop-down arrow in the Action column and choose Make master admin.
Select Make master admin on the pop-up that appears.
An invitation email will then be sent to the user to accept the role.
If the new admin is not a QuickBooks user yet, you'll need to add them as a new user. Once done, you can follow the steps above to transfer the role.
For QuickBooks Online Simple Start, you'll need to get in touch with our support so they can change the master admin for you. Click on the QuickBooks Online (QBO) drop-down to see the most updated support schedule: Support hours and types.