If you have deactivated the check mark which deletes all documents when deleting the document app, you will find the documents as follows:
- Go to "My files" at the top of your profile picture
- Then click on the house symbol on the left
- Navigate to the workspace or page on which the app was available
- Select the folder of the deleted app
In this folder you will find the documents.
If you have deleted a single document, there is unfortunately no way to restore it.