To make changes to one of the scripts written in Javascript, just make a pull request. (Feel free to raise an issue to discuss first)
To make changes to one of the scripts written in Typescript:
(1) Download the repository and run npm install in the userscript folder
(2) Make code changes inside the /src folder (not the /dist folder)
(3) Run npm run build
(4) Paste the newly built userscript from the /dist folder into your userscript mananger, and verify that it's working as desired
(5) Make a pull request
For tips developing userscripts in this repository, see Dev Tips.