How do I request a Modification Proposal?

I have seen users posting Service Modification Proposals (SMPs), but I do not know how to propose one.

I tried searching this forum for any guides, but I did not find anything.

Can someone who knows how to make SMPs provide a guide?

on the desktop website there is a “Propose Service Edit” button at the top nav bar

yep, here is the link ToS;DR Community