How do i customise the icon on mobile homescreen?

Dear Sir

Many of our users will bookmark/save the form site on their mobile homescreen - iOS and Android.

How can i customise the icon - rather than displaying the default pencil icon? thanks.

As far as I now, you would need to use an app to be able to do so.

I did a little research and found the following apps for Android: https://play.google.com/store/apps/details?id=com.jy.iconchanger.ad&hl=en and iOS: https://itunes.apple.com/us/app/app-icons-free-cool-icon-themes/id749073889?mt=8

Let us know if this is what you're referring to.
Thanks.