How can I make my biology part strong though I am able to solve physics but forget something in the botany part??

First you should make a time table as you are weaker in biology then you should study of the subject more than that of other subjects. You should read the chapter twice and you should mark the difficulties and you should clear it them by your particular teacher.

Hii

To improve your biology part you need to by heart the NCERT book, the diagrams, facts, and line by line you must know the details. So you need to practice the biology questions. Solve the sample papers, previous year papers for biology. You can buy a book that will have the chapterwise and topic wise questions for practice and also include previous year questions.
I can provide a link with best books. https://medicine.careers360.com/articles/best-books-for-neet
All you need is practice, practice and practice. you will become expert till neet exam if you practice honestly.

Hope this helps.
All the best!!!