I think you are looking to install and enable particular extension(s) from the collection of community-contributed unofficial extensions that add functionality to the Jupyter notebook so they are active in your launched sessions? The current example page for doing that via MyBinder can be found here.
Personally, I prefer the older version that offered installing and enabling more extensions here; however, because not among those worked in both classic notebooks and JupyterLab, it was streamlined to ipywidgets which works in both. In case your situation ends up being tricky it may help to see some other examples. I can also offer an example documented here (linked to from discourse here) where getting the hide_code extension working in a complex set-up took some extra effort.