After the file is deleted from the Documents app, it will be placed in the Recently Deleted folder; you will have up to 30 days to restore deleted files. To restore the files from this folder, open it > select the file > tap Put Back in the lower-left corner of the screen. You can also tap Move to choose the folder you'd like to put the file into.
If you delete the file which was located in an iCloud folder of the Documents app, you can also restore it on the iCloud webpage > iCloud settings > Restore files section. If the file was in a synced folder, please check the Recently Deleted folder within your Documents app.
If you deleted the app itself, you can try restoring your device from the backup or restore specific files from the iTunes backup using iMazing software on Mac/ PC (or any other software which allows browsing the backup) without restoring the whole device from the backup.