CoSMOS Gamehacking Tool

I am trying to hack Valthirian Arc: Hero School Story to increase the Experience gained at the conclusion of missions. In the .NET Assembly Viewer I found the exact line of code that I want to change (in AssemblyController:OpenReward). It adds the experience from the mission to each student. I opened the assembly viewer for that method and am having trouble finding the corresponding lines of code. I think it would be easiest to add a multiplier to the experience gained, but replacing it with a fixed value would work as well.

As this is my first time hacking a game (other than simply searching for values) and my assembly being quite rusty, I am not sure how to inject the new code even once I find it. What would be the best resources to lookup to figure out how to do this?

Thank you,