The first step would be to set a variable.
The second would be to add the variable to the stat chart.
The third would be to add the *set weight +5% increase in the code.
You may want to experiment with [Tool] Chronicler - ChoiceScript Visual Code Editor if you are hitting some snags. I feel like using this visual flow chart has helped me keep my game organized as it is very easy to create variables - and then manipulate them. CJW is also working on creating a program that will allow easier building of your stories - CSIDE.