Can somebody help/guide me to learn sap mm from scratch.

Suggest me some course/training, paid/unpaid or may be youtube/learning tutorials. I am having 1.2 years of experience in Coupa. Previously i was into manual testing for 5 years. I just wanted to move from technical to some functional role. When i was on bench i got this opportunity for reskilling in coupa.

Can you all guide me staying in coupa is good or not. *coupa is a business spend management tool, related to supply chain.

Please help.