If the previous patent has been granted, then if the modified product wants to protect the improved part, it should apply for a new patent. Only in this way can a tighter protection be formed. Because the former patent protects product A, and the latter patent protects technical solution B that is an improvement on product A, the scope of protection is different.
If the previous patent has not been authorized, you can reapply for a patent and claim the priority of the previous patent for improvements made within 12 months of the previous patent application date, and the previous patent will be withdrawn. , the re-applied patent obtains a relatively complete protection scope A+B.