Hi there ac791,
Thanks for reaching out about your supplier credits. QuickBooks Online is a great tool able to help you keep track of bills, payments and credits so you know the amount owed. I can point you in the right direction with assistance in writing off these credits.
To know how you should be treating these credits that you won't be using, I recommend reaching out to your accountant. They'll be able to best guide you in getting rid of the credits so your books can be accurate. You can invite your accountant to your QuickBooks Online account by clicking on the My Accountant tab. There's also an option to find an accountant near you in that section by clicking on the Find a Pro to help button.
If you have any other questions, feel free to reach out here.