This is a great question, Cesar. The unfortunate reality is that courses in systems are not as common as they could be. This is part of the motivation for this site, actually. So, assuming you can't find systems modeling courses at your home institution, I can see 2 broad options.

Firstly, there are some online courses you can take, largely not for credit. Some of them are shown in this site in the Online Resources section. Dr. Nate Osgood also has a wealth of information here and on his YouTube channel. Also, this site includes a short course that was developed by a number of systems experts. It contains lecture material, sample models, and a teacher's manual. (It is "Systems Course" in the More dropdown.)

A second option is to find short courses you could attend. Perhaps with some creativity, you can arrange to achieve some official recognition or credit for taking these. Dr. Nate Osgood has a yearly bootcamp in Canada. I heard of a couple systems trainings that took place this summer as well that perhaps occur regularly. I know that Dr. Peter Hovmand held a course this year. I can reach out to some colleagues for info on these courses and post them here. Perhaps you could contact them directly to see if they are holding future courses.