Hello Gary,
You may be able to manually launch the program by searching it from the start menu, once the app launches the icon on file explorer should return, if not try the following.
Try resetting the OneDrive sync app:
1. Press these two keys on your keyboard at the same time: Windows key and the R key. This will open the Run dialog box on your screen
2. Copy and paste this text into the Run window and press Enter:
%localappdata%\Microsoft\OneDrive\onedrive.exe /reset
Let us know how it goes.