Completing 12th grade, there are several ways to become a software engineer. One is by pursuing a degree such as BTech/BSc in Computer Science or IT. Another way is to acquire skills through online courses, coding bootcamps, etc.
Firstly, you should learn the basics like programming (Python, Java, or C++), data structures, and problem-solving. Then you can develop some small projects, keep practicing coding, and finally, apply for internships or entry-level jobs to gain real work experience.