Look for some kind of self-help group, course or training in "presentation skills" or "public speaking." Nervousness when presenting to a group is very common and sometimes very severe. It can be partly overcome by practice, particularly in a sympathetic group of other people who are trying to do the same thing.
I would recommend an organization called Toastmasters, but they are harder to find outside the United States. Still, I searched on their website and found six Toastmasters clubs in Rio de Janeiro and eight in São Paulo.
Maybe you can't make the nervousness go away, but you can learn to make good presentations despite the nervousness.