A license needs to be changed without uninstalling the Point of Sale software.
To change a license number from a disabled number to an enabled one without uninstalling and reinstalling, run a repair installation of Point of Sale. You will be prompted for license numbers during the process.
How to change a license number link
If this solution does not resolve the issue, you can read discussions and post messages and questions relating to your issue on the Intuit QuickBooks Community site. You can also review other available QuickBooks Point of Sale support options for additional guidance.
Here is a link that tells you how to repair your installation of QuickBooks POS.