Hello. I am Christine, the accounting supervisor of SifFO US.I want to be admin user. Other people have left SiFO US.

Do you have any access to last master admin's email address? You may try reset the login password of QBO, login to QBO with that master admin credential, then change the master admin role to yourself. Otherwise, you have to call Intuit directly to claim your account.

Welcome to the Community, @catherine_huang.

@Fiat Lux - ASIA is correct. We can try to reset the login password. Just go to accounts.intuit.com and select I forgot my user ID or password at the bottom.
 
Once, you'll be able to log in, I recommend the following article for additional information on how to transfer rights: How to Transfer The Role of Master Administrator.

Also, if you don't have any access to the account, I suggest contacting our Customer Support Team. An agent will assist you by gathering the necessary information to complete a Master Admin claim. Once the claim is finished, the rights will be transferred to you.

Here's how to contact our Support Team:

1. Sign in to your QuickBooks Online company.
2. Click Help (?) at the top right.
3. Select Contact Us to connect with a live support agent.

You can get back to this post if you have further questions. The Community Team and I are always here to help.