Filling in surface using cylinder as boundary

Hi, I’m new to sketchup and I am trying to close the bottom rectangular surface which intersects the thin cylinder partway down its length.

Thanks heaps for the help!

Could you upload the model? From the image I can’t figure out what you mean…

I want to close off this part. How do i upload the model?

Provided the model is <3MB, click this button in the reply edit window:

One way…