Rastrigin's Function For GA

Hi. I am new to coding, but I have a GA (not written in MATLAB), and I need to find the minimum for Rastrigin function. I have read about optimtool('ga'), however, do I need to call my own GA code in order for it to work? If I have my GA written, but not in MATLAB, is there a way I can calculate the minimum?

If so, step-by-step instructions would be most appreciated. Thank you so much.