From the Bill Pay main screen, click on Options below the name of the payee you would like to pay from a different account. In the picture example below, to change the account from which you pay Jays Plumbing, you would first click on Options directly below Jays Plumbing.
On the Options screen, click on the Account Information tab. Click on the blue link next to From that displays your default checking account for Bill Pay. In the drop-down list, select the account from which you would like to pay this payee only, then click the Save button in the lower-right corner. Important note: this will only change the paying account for this payee. Your other payees will be paid from your default account unless you change the default OR change each payee individually.
When you are finished editing, please click the Save button in the lower right-hand corner.