I see Jaison Jose posted the solution first. And it worked for me, while although the first appearing answer here shows the same solution with more steps and info, it did not start the update process. Maybe it had to be run twice or some programs were still closing, although I looked through Task manager and closed the Office click-to-run.
Since I already had tried to fix the problem myself and had managed to restore the functionality of the Taskbar icon, I ran into some issues after the downgrade. Excel complained about spreadsheets not associated on each clean run, even after I did a Quick Repair. Looking at the per app list and the per file type list I saw all (including for Word) were associated correctly to the app, no more mentions of appvlp. However the recent list from the Taskbar icon refused to open any file saying it didn't exist. A simple check with the right button there and Open showed it's not true and the files opened this way. I had to remove the icon from the Taskbar again and re-pin it from the on in the Start menu. Then all files started opening fine again. meanwhile I set Open with for xlsx and xls from Windows Explorer manually to Excel with the option to save this setting.
I hope this info helps, if you have issues after downgrading.