Problem with text mesh pro after updating to unity 2018.2

Before I was running 2018.1 and it was working fine, after I updated to 2018.2 I get this error: Assets/Asset store/TextMesh Pro/Examples & Extras/Scripts/Benchmark01_UGUI.cs(14,16): error CS1070: The type `UnityEngine.Canvas’ has been forwarded to an assembly that is not referenced. Enable the built in package ‘UI’ in the Package Manager window to fix this error. How do I do this? If I can’t get this game working again it’s a year and a half of work down the drain!

No one cares, no one.