[AC Question]

How do I add an app to the existing list of messaging attachment options within the default messaging app on galaxy note 4?

[Tim1954]

You want to share an app via messaging? Have I got that right?
Some apps have the option to share, usually it will be a link that takes the recipient to play store etc...

[ManiacJoe]

If you want to add an app to the message, you just add the URL to the Play Store entry for the app.

If you want to add another app to the "use app to find file" list of apps, that should automatically happen when you installed the app.

Which version of android are you running?
Which messaging app are you using?
Which file type to you want to add to the message?
Which app is missing from the "use app to find file" list?