Many institutes offer GST coaching, to be honest they are all minting money.
Why you need a course when you can learn everything about GST online.
There are many free videos and articles available. Visit KnowyourGST daily and read as many articles and questions.
Even if you do not understand anything, just read them.
After a week or 2 you will start getting an idea and than read GST acts like CGST Act and IGST Act.
If you get any doubt ask on QA platform.