All my files are not available ?

That’s the App - not the storage location.

Try a forced-restart of your iPad:

• On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
• On an iPad with Face ID: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.

Which files? Are they local stored on your iPad - or in iCloud - or some other cloud service?