First step is to speak with the career advisor make sure your current AFSC can release you and that you are in your retraining window. Depending on where you are stationed (as of now) spec ops recruiters cannot give you a PAST test. So you will need to travel to a base with a STS or RQS on it and have them conduct a PAST test for your package. Keep in mind, don’t do this too early because they are only valid for approx. 6 months.     

You just put it on your assignment list, and make sure you’re a good candidate. The 24th STS has an additional selection. But to be honest you need to focus on becoming a PJ first. The 24th is a long ways away.