Hi there, @gail34. I'll share information that will give answer to your concern.
To batch change the suppliers that has been coded with the same nominal codes, you'll have to invite your accountant for that. They can guide you and advice you more specifically on that matter.
Another option is you'll have to edit the transactions one at a time.
Additionally, you can read through this article for more information about importing your customers and vendors: Import customer or vendor contacts from Outlook, Excel, or Gmail.
I'm also adding the following articles in case you'll need them in the future:
Please let me know if you have any other concerns or need any further assistance in setting up your vendors or customers. I'll be around. Enjoy the rest of the day