Q:

I need help changing the default URL for SharePoint in O365

When I log into my corporate O365 account, I get the screen with apps I have access to.  When I click on the SharePoint app, it does not take me to my corporate SharePoint Home page (https://avistapharma.sharepoint.com/Pages/Home.aspx)
it takes me to a page (https://avistapharma.sharepoint.com/_layouts/15/sharepoint.aspx) that shows me the last few sites I've visited on my corporate page.  I need to change the URL so that when I click on the SharePoint app, it takes me directly to my corporate home page.  Does anyone know how to do that?

A:

Unfortunately, this tile and other OOTB tiles app launcher experience is controlled by Microsoft. So we dont have the ability yet to modify the tiles or its behaviour other than of course the theming(color) part. 
So we will have to wait till MS (and if) provides us the capability to change the experience. (IMO, not anytime soon). 

One thing you can try is by adding your custom tile to the app launcher using global admin credentials. Unfortunately, this cant be pushed to all users, yet, so each user will have to individually pin the tile once admin after admin has added to the app launcher.
Add custom tiles to the app launcher
How to add a custom Tile to Office 365 App Launcher

