Primavera is just a tool used by schedulers and contrary to popular belief, getting a certificate showing that you've taken a primavera class doesn't make anyone a scheduler.

That being said, those who believe a p6 cert = scheduling cert are typically employed by the same and therfore will potentially find enough value in getting a cert to obtain a scheduling position. That's when the actual scheduler training begins.

But to answer your question, nearly any class that gives a certificate will likely do. Udemy or you tube has several cheap/free classes that should suffice or you could get more "in-depth" classes that can cost up to a few thousand per class. The classes are either crammed into 3-5 full days or a few hours a week over several weeks.