Typical student jobs in restaurants or cinemas are currently scarce due to the Corona crisis. With the paid internship it also does not always work out. If your parents can't help either, you should look into government aid. For example with the student loan.
Since June, the Federal Ministry of Education and Research (BMBF) has been offering students a grant of 100 to 500 euros as a bridging allowance for pandemic-related emergencies. To do this, you'll need to apply to your student union – the easiest way is directly online. The grant does not have to be repaid. However, it is envisaged that it will exist until August 2020, and that it must be reapplied for every month. If you haven't applied for it yet in July, you should hurry now.
Interest-free student loan from KfW
If your primary residence is in Germany, you are between 18 and 44 years old and have not yet studied more than 10 semesters, then you have a very good chance of receiving a KfW student loan. It is still important that your university is state-recognized and that you are studying for a state exam, bachelor's, master's or diploma degree. The student loan of a maximum of 650 euros per month is available regardless of your parents' income – and even at an interest rate of zero percent until March 2021. The Federal Ministry of Education will pay the interest for this period. Read more on KfW's website.
If your parents now have less money available due to corona, you should apply for Bafog update. But beware: the decreased income must be proven. If you have given too low a sum, you will have to pay back money in case of doubt. More information is available on the Bafog page of the Federal Ministry of Education and Research.
Apply for housing assistance
It won't make you rich, but housing assistance will help lower your rent costs. The money freed up as a result can then in turn be used for living. More about housing benefit at the Federal Ministry of the Interior. Alternatively, of course, you could save the rent by temporarily moving back in with your parents.
This can make sense if they live close to the university anyway and commuting is acceptable. Or if it turns out that the winter term will also run primarily as an online term. Depending on where you study, it will be difficult to find accommodation afterwards. To save money, you could also look for a room in a shared apartment. A sublease is also usually a favorable solution.