If the question is; "Agree with me that Carrara lacks a tool I think it should have," then there isn't much point in trying to be helpful.  Sure, Carrara could use more tools.  And better versions of some of the ones it has.

If the question is, on the other hand "I have a modeling task and I'd like to try to do it without leaving Carrara," then there are answers.

For me it would be a couple of steps.  Marquee to select one edge of the item, edge tool to select and extract an edge and drag it to approximately where I wanted it, and then scale tool to make it planar.

I've done the like many times.