I am setting up quickbooks and I forgot to put in starting balance for my supplier before putting up a bill and now it wont let me

Welcome to the Community, @userbbrady.

There are two ways to how correct this.

If you only created a single bill, you can delete it and edit the opening balance from the supplier's profile. Let me show you how: 

1. Sign in to your QuickBooks Online account.
2. Go to the Expenses menu and then Suppliers/Vendors.
3. Choose the vendor, then click Edit.
4. Enter the opening balance.
5. Once done, click Save and close.

If you wish not to delete a bill, you can enter a different bill and use opening balance equity as the account for the expense. Make sure to put a reason in the Memo box and then enter the starting date of your company.

I've also added this article that can guide you make a bill payment in QuickBooks Online: Pay bills.

Feel at ease to let me know if you need further assistance with the process. I'm more than willing to help. Have a great day.