I am in 2D Layout. How do you change a measurement after a rectangle is created? I select the rectangle but not able to type in measurements box.
Use Scale tool and type the new dimensions and units

I tried the scale tool but am not getting the grips to change size
Have a go at the basics and learn the fundamentals, some of which may vary slightly depending on which version you are using.
https://learn.sketchup.com/
Thank you I will try it.