Select the menu (next to 'Play') > Manage installation > Verify / Repair .
For Steam users, you can verify the integrity of game files through Steam to ensure Skyrim.esm is present and correctly installed. To do this:
Right-click on (or Special Edition). Select Properties . Go to the Installed Files (or Local Files) tab.
Verify your game files through Steam (Right-click Skyrim → Properties → Installed Files → Verify integrity of game files). Steam will redownload any missing or corrupted base files, including Skyrim.esm .