For clarity.
"Pushing" refers only to a change in development. What you have is a roll where some of the frames have been exposed normally, while others have been under-exposed by as much as two stops.
If you push the development, you:
1) increase the contrast of those parts of the image that actually registered on the film; and
2) make the highlights more dense (and potentially too dense); but
3) you do almost nothing to retrieve the shadows that you lost detail in due to the under-exposure.
The answer to your question depends at least partially on the scenes you under-exposed when they were photographed. If they were full of dark shadows that you wanted to maintain detail in, there is basically nothing you can do. If, however, there were lots of important mid-tones and highlights in those scenes, and you can afford to lose the details in the shadows, then a push development may help.
Make your choice between a one or two stop push depending on how contrasty the lighting was, and how important detail in the highlights is to you - in both the properly exposed and under exposed portions. The more important and contrasty the highlights, the more important it is to minimize the push.