Hi Varun,
Not clear with your requirment as per my understading your able to assgin the extended app user as mentioned in blog How To Deploy an SAPUI5 App On Fiori Launchpad
I am not frontend developer but If you want to create custom tile go through Creating custom tile in sapui5 using sap.m.CustuomTile and use Press event and naviagte your extended app.
If not please share your requirement indetail.
Thanks,
Lakshman Balanagu.