Q.How and when should I trim my rubber tree?
A family member had a rubber tree that had several stalks in a pot. One of the stalks was taken out and given to me. I have had the plant for three years now. It has lots of new growth on the top of the plant; however, the bottom is bare. I usually keep it in my office near a window but for the past six days or so it has been outside. I know I should not change its location too much; however, I wanted it to get fresh air. Should I trim the plant to make it flourish out, or will it grow out on its own? How do I thicken it up? Thank you in advance for answering my question.

Wow! Thank you Shelley, this is some great info.

When a rubber tree is single-stemmed it is advised to wait until it is two feet tall at which point you can prune it to half its height. You will make your cuts just above a node — where the leaf attaches to the stem or where another stem branches off.
This article will help you:
https://www.gardeningknowhow.com/houseplants/rubber-tree/prune-rubber-tree.htm