Are you trying to change your payment account in your bank? In QuickBooks Self Employed (QBSE), changing the bank account for manually added transactions isn't possible. Please know that the transaction will automatically post to the Cash account by QBSE (the default account).
Since you want to post the transactions to your bank account, you'll need to connect your bank to QBSE. Here's how:
Sign in to your QBSE account.
Click the Gear icon, then select Bank Accounts.
Search for your bank and enter the sign-in info you use for your bank's website.
Select Connect securely once you're ready.
If you're trying to update the deposit account by logging in to your QuickBooks Payments account. I'll guide you with the steps.