I don’t have steam so it makes it difficult.
Let’s do it this way
go into MSFS2020
Select Options
Select General
Select Developers (on the left, at the bottom)
Turn Developer Mode on
Look for the new menu in the top left (the text is very small)
Select Tools
Select Virtual File System
In there you will find Open Official Folder
Click on that
You will find Asobo-aircraft-b787-10 in there.
Cut it and paste it somewhere (say desktop for instance)
Close sim.
Start sim again.
It will make a new one.