Do you speak Spanish?
Honestly I wouldn't know where to direct you, but maybe find in Germany organizations that provide help to developing countries (like those in Latin America) and see how you could volunteer. There's a plenty of places where you're help could be used assuming you speak Spanish. English can get you only so far, in only to work in the places where volunteers are needed you'll have to work on your Spanish.
I volunteer during dental school, I just showed up at the hospital dental department talk to the doctor in charged and told him what I wanted. The same I did here on the US.
In your case, try to find an organization that guides you like Rotary Club, religious organizations, research programs (find cleft lip and palate research projects, there's plenty of those).
Try to find a guide trough private parties, government officials know nothing about it.
Good luck, I wish I could help you more.