how would one properly test a change and make a pull request?

I’ve made a simple change (giving salv extended capacity survival boxes) but I dont know how to test if it worked or how to make a pull request and what exactly I need in the pull request (I assume its like modding left 4 dead 2 where you leave out what you dont want changed, which seems a little obvious)

for building see

to make a pr just git checkout -b funny-branch-name then add and commit your changed file(s), push to your repo and make a pr with the link it tells you or on the website