Thanks everybody for your help and your time! It's been really helpful!
To summarize:
-Go to the airport while avoiding being caught
-bring 20 000 thai money and I negative covid test
-go to the immigration desk, pay the fine and come back to Austria.
-no lawyer needed
Btw he is not my friend but a relative -brother in law- (For everyone who called him my friend). But that's just a detail
Ps : he is not the guy that police caught today, his flight is next week
Thanks again everybody ????????