Remove the previous owner's company address from our registered address

Contact each portal individually? That would certainly take longer than 3 posts here in the forum.

But it would be more effective, since the portals do not crawl through forums to see if they are mentioned there ;-)

But it would be more effective, because the portals don’t crawl through forums to see if they are mentioned there ;-)

That’s why the question is whether I can, for example, approach the district court "once and for all" (and the portals will catch up eventually in 100 years).

That's why the question whether I can, for example, turn to the local court "once and for all"

Check the commercial register online, there you will find out which registry court is responsible. This is by no means always the one in whose local court district the company has its seat – the courts are organized somewhat like the tax offices as competence centers. You notify this court that you have the sole authority of disposal over the building named as the company headquarters and that you are not the landlord of the company. You then notify the same to the trade office of your municipality. I assume it is known that one writes to authorities only with delivery confirmation. You can also provide both with the last known place of residence of the managing director. [Personal opinion – not legal advice!!!]