how to clean junk files in ipad?

iOS takes care of its own garbage collection. There is no need for a separate app.

Since each app is limited to its own sandbox, there is no app that could do what you

desire if one existed.

If you have a specific problem in mind that make you think you need something to clean

junk files, provide more detail and someone will offer a solution.

I Have a 64 gb iPad air

THere is about 30 gb difference between the storage used and the storage remaining.What I'm saying is that,if I add up all the storage used its about 20 gb

I should have about 36 gb free,but only have 8 gb remaining.

THere are clearly junk files.

I can't do a full restore as I have downloaded films to VLC which,for some unknown reason don't back up to iCloud