Window fix

Hi all, almost a month ago, I asked here about what to do if my landlord doesn't fix the issues and people suggested Einschreiben. After 3 weeks, no fix, so now I need to find someone to fix my window which doesn't close fully (shared a video for more clarity) and then send the invoice to landlord. But, I don't know who to call, or what to Google to fix this issue, most of the results from Google is window installation companies. Can you share please what to Google or what kind of company I should look for?