How to make a performance test bulk registration?

I have an application where course participants at the end of their live-training register. This means each participant opens a url like www.my-example.com/register - these are about 50 people at the same time. It appears, that my server is too slow to handle 50 people at the same time.

I do have a written HTTP Tests in Laravel for a single registration, but how can I simulate that this happens 50 times in parallel? So I can check how the experience currently is and if I my changes make an impact.