You can keep reviewing the skills until you get all of them to crown level 5.
You can do the "reverse course" - in other words, learn English as a German speaker. You'll do more translating into German, an all of the sentence discussions will be in German.
Congrats on finishing!
Do you mean that you have finished each skill in a language tree? If that's the case, you can progress further with that language by advancing all the skills to level 5 (which would make them gold) and keep learning!
According to https://www.duome.eu/JimTynen/progress, you're not finished with your German course. You are close to finishing each skill at the one crown level, but the strength of many of the skills are significantly atrophied.
First, bring the entire tree to five crowns. Second, bring the strength of each skill to 100%. Once you've done that, then you can stick a nail in the tree and call it complete.
Then, assuming you want to improve your German skills past the A2 level and on to the intermediate levels, you'll need to find other sources to work with.