How to mass erase all iPad Air 2 emails

I have over 9000 emails on my iPad Air 2. I do not want to erase one at a time. I can not find a method of erasing all at the same time

At the bottom of the screen all I see is [Mark All] highlighted (which I have done) but the [Move] and [Trash] are not. They do not come on when all the emails have been Marked All.

Is there a method that I have not come across yet?

Thanks for any advice.

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