Hello,
Yes, you can become a doctor after you have completed GNM course. You will have to pursue MBBS in order to become a doctor. The process is simple, you have to fill the application form for NEET UG and prepare and work hard to clear thebcut off of a good medical college (government college, preferably). Since there is no upper age limit to appear for NEET UG, you won't face as much problems.
You can go through the link below to get more information about NEET UG:
https://medicine.careers360.com/articles/neet-2022
I hope this helps,
All the best
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