Thank you for reaching out to us!
Could you please be more specific about your situation?
I've had a look for general information on working permits in Germany and how to extend them. The following links should provide all the information you need:
1. The Berlin Service website includes plenty of information on residence permits for the purpose of employment (if you scroll down, it mentions when you should start the extension period and how much it costs). The information can vary depending on the city/ area you live in - this one is Berlin specific: https://service.berlin.de/dienstleistung/305304/en/
2. A website on Germany Working Visa: https://www.germany-visa.org/work-employment-visa/
3. And the same website with a more detailed explanation of working in Germany (what to be aware of, which visas you can get, etc.): https://www.germany-visa.org/working-germany-getting-german-work-permit/
I hope this information helps. Feel free to reach out to us again with more information if you need any further assistance!
All the best,