Fast stop to learning unity:error cs0234

just started to use unity and both in my school computer and my pc the same error keeps popping up, can someone with more experience give me a step by step fix?
‘‘Assets/Standard Assets/2D/Scripts/Platformer2DUserControl.cs(2,25): error CS0234: The type or namespace name CrossPlatformInput' does not exist in the namespace UnitySampleAssets’. Are you missing an assembly reference?’’

Sounds like you’re missing a script called CrossPlatformInput.cs. Try reinstalling the Unity standard assets and making sure you include that script, or if you are not using Platformer2DUserControl.cs then remove that script.