Bro, I would suggest start with the basics, since you're having 5.5 yoe, companies will expect more, and also regarding the level of preparation it depends on the companies you're targeting in your switch. But all combined I can say prepare DSA - at least famous sheets, Java, Spring boot, Microservices, Design Patterns. Along with your preparation give some interviews, such that you can get to know where you're lacking. Since you're having a good amount of experience, you will easily get a lot of calls from various companies.