If your friend wants to be a CELTA-qualified English teacher, then they need to complete a CELTA teacher-training course.
They can do this one month full time, or part-time split over a few months.
The website
http://www.cambridgeesol.org/teaching/celta.htm has more information on the course and where it can be completed in Switzerland.
Note: the course seems to be a lot more expensive in Switzerland compared to other countries.
There are some other threads in this forum on CELTA - maybe they would have some usefull information for your friend also.