Hi, I use QuickBooks online Plus and i will like to add another account(expert) that i can transfer subscription and billing functions to. what should i do?

I'll provide the two options for this, @lucky-adesunloye. 

If you need to transfer your Master Admin role to another expert, it depends if they're a new or existing user in QuickBooks Online. This way, the subscription and billing functions will be theirs. 

For the new user, these are the steps: 

1. Sign in to your QBO account as the current master admin. 
2. Go to the Gear (⚙) icon at the upper right.
3. Select Manage Users under Your Company. 
4. Click Add user.
5. Choose Company admin as the user type.
6. Click Next.
7. Enter the new user's info and click Save.
8. Your new user will get an email from quickbooks-email@intuit.com inviting them to your business. They need to select the Let’s go! link and sign in.
9. Please follow the steps below to make the new user your master admin to complete the process. 

For an existing user: 

1. Go back to Manage Users page. 
2. Check if the user you want is listed as Admin in the User Type column. If not, select Edit to change them to an admin.
3. Select the small arrow ▼ in the Action column to the right of the user. Then, click Make master admin.
4. Choose Make master admin to confirm the change. 
5. Go to the Gear (⚙) icon at the upper right and select Sign Out to log out as the current master admin.
6. When the user gets the invitation email, ask them to select the link and accept the invitation.

To learn more about the process above, check out this article: Change Your QBO Master Admin User. 

After that, your other expert can now manage the plan info in the Billing & Subscription tab. They can perform some of these tasks, such as updating the credit card info, upgrading, or downgrading the subscription. 

If you want to open another QBO account, go to this link: https://quickbooks.intuit.com/choose-country/. Then, select your specific country and click Buy Now or Free 30-Day Trial to subscribe. Complete the signup process afterward. 

Once done, I recommend visiting this link: Global Help Articles. It contains a list of articles that'll help you effectively manage your QBO account and other essential tasks.

Click the Reply button below if you have follow-up billing concerns or other inquiries. I'll gladly help. Keep safe.