Welcome and thank you for posting here in the Community page, @forbygrace66.
If you're referring to changing a vendor to a bank account in QuickBooks Online (QBO). We don't have the option to change a vendor to bank account, however, you can make the vendor inactive and create a new account.
To create a new account:
For additional reference, you may check this article: Create a new parent account or sub-account.
Feel free to add a comment below or click the Reply button if you're referring to something else. Have a good one!