It really depends how you moved MSFS. The only method that is safe and proper, which GSX supports, is the official one, that is moving the whole Content folder and changing the UserCFG.opt file. What matters is the Content (the big Official and Community folders), not the MSFS installation folder itself, which is small, and doesn't matter for GSX.
Assuming you want to move the MSFS Content
for example D:\MSFS (assuming the new drive is called D:), so you'll end up with this:
D:\MSFS\Community
D:\MSFS\Official
Once you done that, you must edit this file:
%APPDATA%\Microsoft FlightSimulator\UserCfg.OPT
Go to the LAST line, and change it as such:
InstalledPackagesPath "D:\MSFS"
This again assumes you placed your Community and official folders there, as in the previous example. This is the only correct method to move the MSFS Content without reinstalling the whole sim from scratch, any other method, like moving just the Community and make links, is wrong, and won't work