Previously, when I wanted to change the files myself, I encountered the same problem and I deleted the game with its root files, but it did not pass, but the solution I will explain below will help you.
*Open Steam, go to the LIBRARY -> GAMES
*Right click on Euro Truck Simulator 2 and open Properties
*After the Properties window has opened click LOCAL FILES tab and press BROWSE LOCAL FILES
*A folder with game files opens. Remember the path to this folder
*Click Start > Run (or WIN+R)
*Type regedit and hit enter
*Follow the path HKEY_LOCAL_MACHINE\SOFTWARE\TruckersMP
*Look at the value parameter "InstallLocationETS2"
*Copy the folder address from STEP 1
*Change the value parameter "InstallLocationETS2" (Insert the copied folder address)
I believe your problem will be solved.
Have a nice day.