Yeah, @fredrik.coulter is referring to How to help with missing/broken cities/regions as the list of where you can add requests.
I generally approach things at the country level - determine which OSM admin level all the Regions (in the US these are states, other countries can use different names) exist at and then from there, determine which OSM admin level all (most) the Cities exist at.
I can bulk-import a country fairly easily that way. From there, I wait for people to complain. 
The complaints are usually that something is missing. If someone asks for it, I generally add it - I don’t put too much personal preference on it.
This does add the issue of then someone requesting that something be removed - perhaps one person does want a large city broken into its smaller pieces (e.g. Manhattan) and another doesn’t. Oh well, can’t please everyone.
It does also add the issue of “duplicate streets”, where you run one street that exists in two separate cities in CityStrides (again e.g. Manhattan). That street is counted as completed twice for you - once in each city. I need to fix that - I think I’m going to add the ability for me to mark some cities as “child” or “contained” or “partial” (unsure of the name, obviously 
) … this would cause those streets to not be counted in the overall count / challenges / etc, but wouldn’t remove the ability to track your progress within that “child” city.