Hi @AntonioRojas01, welcome to the forum!
The problem is that pycharm is trying to use its own virtualenv package, which is written for python 3.
You have to create the virtualenv by yourself outside pycharm, then add it to pycharm using the “existing envitonment”.
But if you use python 2.7 only for pyrevit, you can skip the virtualenv and directly add the path of the python executable you just installed