The DLL will be restored to C:\Program Files (x86)\Steam\steamapps\common\Resident Evil 4\Bin32\ (or your custom install path). Launch the game.
When confronted with this error, your first instinct might be to search for "download steam-api.dll resident evil 4 uhd" and grab the file from a third-party DLL repository. download steam-api.dll resident evil 4 uhd