Closing hollow tubes

I’m extremely new to Blender, but having a lot of fun getting into it.

I am trying to develop a concept where I’ve taken the torus and cut it half facing from the top view and separated the two halves. However, I’m left with hollow tubes for both ends of the 2 halves. How would I solidify them?

Thanks for your help and patience.

Select the end verticies, ‘e’ to extrude and then left click or hit enter right away, alt-m and choose center.

What they said ^^^

Although I would do two extrude - scales and merge the second one to minimize the distortion if you should choose to add a subsurf in the future.