I think it was asked in here - someone looking for a suitable material
to fix a chipped w/basin and one of the suggestions was this stuff -
https://www.ebay.co.uk/itm/273423238467

I asked if might be suitable for a chip in a white enamelled pressed
steel bath. It was suggested that it was, so I ordered some, which
arrived yesterday and I used it yesterday.

It worked and was much better than I expected. It had set up incredibly
hard by this morning. The instructions though, are a very poor
translation and took several readings to get the full jest of it.