As of now, QuickBooks only allows you to modify sales forms. Thus the option to change the payment voucher format isn't possible.
Please know that QuickBooks has a default format for a payment voucher. I understand that you want to change it back to the old format. While this feature isn't available, I suggest submitting feedback directly to our product engineers. They may look into this suggestion further and consider adding the option in QuickBooks Online (QBO). To submit feedback, you can go to the Gear icon and select Feedback. Then, enter your suggestion and click Submit Feedback.
Also, you can visit our blog site so you'll be able to get the latest news about QuickBooks and what our Product Care Team is working on.
Please keep in touch if there's anything else I can do to help you succeed with QuickBooks. I'll be more than happy to assist you again.