"Review vs in reviewing "
Use "in reviewing" because your main sentence is present tense through the start of "I am...." A good way to compare is to really make it obvious by stating "I am presently thankful...because of your present review." It would be a weirder context if you were to say "I am presently thankful...because of your future review."
This is for a resume, so signal to your reviewer that you expect that the application has already been reviewed.
However, I would still revise the sentence all together. Refer to Mark Hubbard's explanation and suggestion.