Alt Text for start screen Cover Photo?

Hey everyone....looking for info on how to change the Alt text for the Cover Photo that appears on the start screen when using the Modern Player.  I love that you can pick a Cover Photo but I have to be able to change/add the Alt text for it.  Our Cover Photo needs to have some instructional text on it.  Client requires it. 

UPDATE:  I believe I found it.  In the Player editor under "Text Labels" I found "Screen Readers: Start course button on desktop computers" #158.  It has a default of "Start Course".  I pasted in my text.  Will have it tested and report back to see if this works.