City boundary incorrect- what is the procedure to fix/escalate ?

I’m an active editor on OSM adding road names etc, but nothing beyond basic level.

I’ve noted a “City” in South Africa called Germiston may not be setup correctly
A resident of the area has raised this with me on a reverse geocode on nominatim that does not return the city
The returned result:
Porter Road, Sunnyridge, Ekurhuleni Ward 92, City of Ekurhuleni Metropolitan Municipality, Gauteng, 1406, South Africa

its missing the city Germiston

His postal address is Porter Rd, Sunnyridge, Germiston, Gauteng, South Africa

I’ve cross checked and it appears Germiston is a city

looking at other data sets, it appears correct

However when I look at OSM data, its listed as a town and it has no boundary so a nominatim reverse geocode does not pick up this area

When I look at the wikidata on the above town node its also supposed to be a city

I would like to fix this issue, but as my previous editing skills are road level, i’m unsure how to proceed to get this fixed
Is there an official process I need to follow, or should i just try and edit myself (not knowing the boundary of the city)

As you seem to have identified already the fundamental problem is that it doesn’t have a boundary so Nomination would only ever be able to match in on the basis of proximity which is never exact.

The first question would be does it even have a boundary - from reading the wikipedia page it sounds like it might not exist as a separate administrative entity any more as it is now part of the City of Ekurhuleni Metropolitan Municipality so it may not have a precise geographic definition now.

In that case there may now be much you can do - making up a boundary geometry for it is not something I would do but other people might disagree.