Hi lmonroe1473!
You'll want to open/edit the check transaction to be able to edit the check number. If it doesn't have a number yet, just remove the checkmark in the Print Later checkbox and enter the number.
QuickBooks will assign the next available number on your next check transaction.
On the other hand, you can check out the Help articles on the main support page if you need quick references in the future.
Feel free to reach back out if you need more help with checks.