how do i delete app download history

Delete from where/how ? You can't delete any item from an account's purchase history, if you don't want apps to show in the Purchased redownloading area all you can do is hide them : Hide apps for your iPhone, iPad, iPod touch, or Mac - Apple Support

It doesn't need to be linked to a computer, the hiding process doesn't need it.

I can hide apps from the Purchased tab in the App Store app on my iPhone 7 (iOS 11.2.6), swiping from right-to-left gives me a 'hide' button which removes it from that list. That is what you are doing on the phone ?

It's never been possible to permanently delete purchases, possibly due to not wanting people to do it accidentally.

What happens when you try to hide them via your computer's iTunes ? There was a bug yesterday that was stopping it working, but that has apparently now been fixed.