The way to fix this is:
Step 1.
Right click your 'Euro Truck Simulator 2 Multiplayer' / 'American Truck Simulators Multiplayer' .exe file, whether it be the shortcut on the desktop or actual file and then click properties.
Step 2.
If you right clicked it's shortcut, make sure you clicked the shortcut tab.
If you clicked the .exe file, make sure you are on the general tab.
You should see a section say: ( Target: "C:\Program Files\TruckersMP\launcher_ets2mp.exe" ) OR it's custom install path. (Minus the brackets)
What you need to do is on the end of it, add: ( -homedir C:\Users\Michael\Documents\ETS2MP )
It should look something like: ( Target: "C:\Program Files\TruckersMP\launcher_ets2mp.exe" -homedir C:\Users\Michael\Documents\ETS2MP ) If you understand what the -homedir fuction does, feel welcome to change it, if you are worried or don't know what to do, just leave it as it is. If you have a problem, message me on Steam H4ns