To incorporate the French Foreign legion, you have to go to France to pass selection tests.

Please consult the official French foreign legion enlistment webpage for further information at https://en.legion-recrute.com/

To get a visa to travel to France, please consult the application procedure on websites of the Consulate General of France in Johannesburg or Cape Town:

Johannesburg: https://johannesburg.consulfrance.org/-English-

Cape Town: https://lecap.consulfrance.org/-English-