Scarlet - https://usescarlet.com. (Scarlet can get revoked and you might need to wait for the next update and download it again).

Install On Air - https://www.installonair.com. (There's a chance app gets revoked, but you can use it wisely. all you need to do is drop the file and wait. When it finishes it will automatically download it).

To download app using Scarlet first open, then head to Box with Arrow facing down.

Now on top click the same box.

And just choose your ipa file and wait till it download.

when it finishes it ask you (localhost.usescarlet.com, would like to instal BloonsTD6) Click Install and you're all set up!