Go to Settings > Assetto Corsa > Apps and check all "Sol" related boxes (e.g., Sol Planer, Sol Config).
Sol requires CSP to function. Version 0.7r5 is very old, but modern CSP versions (1.76 or newer) are generally recommended for stability. SOL_0.7r5_Win64_.zip
Drag these four folders into your main Assetto Corsa installation directory (usually C:\Program Files (x86)\Steam\steamapps\common\assettocorsa ). Go to Settings > Assetto Corsa > Apps