how do i download the apple music app to my ipad

You provide no details of your iPad model - or the installed version of iOS. The tags appended to your post suggest that you have an iPad4 with iOS10 installed.

Older versions of iOS include the Apple Music App; as such it can neither be removed nor independently installed.

Newer versions of iOS/iPadOS do allow removal and/or reinstallation from the Apple App Store:

https://apps.apple.com/gb/app/apple-music/id1108187390

The current version supports iOS 10 and up. Just search for “Apple Music” in the App Store and download it.

https://apps.apple.com/us/app/apple-music/id1108187390