Hey there, @amy10.
It's great to see you back in the Community. I can point you in the right direction to set up a new merchant account and cancel one from the other QuickBooks Online account.
To get this successfully to work, reaching out to our Customer Support Team is the best route at this time. They'll be able to give you some more details, plus walk you through the steps.
Contact Payments or Point of Sale Support
Keep us updated on how it goes. It's my priority that you get this figured out as soon as possible. Take care!