Knowledgebase:
iPad Locked - How to perform a hard shut down
Posted by Respondus Support
If your iPad is locked up, we recommend you perform a hard shut down. To do this, hold down the Home and the power buttons simultaneously for 20-30 seconds.
If using an iPad Pro, follow the steps provided by Apple, found here: https://support.apple.com/en-us/HT210631
 
For further assistance in how to force an iPad to shut down, please contact Apple support.