Hello Pratibha,

You can start to learn graphic designing for free from different platforms like youtube, Coursera, Udemy etc for entry level.

You can aslo enroll in different institutes for graphic designing courses of different durations ( 3 months to 1 year) .there are numerous institutes which teaches graphic designing.

For diploma you can apply in institutes like -

1. National institute of design, ahemdabad.
2. National institute of fashion technology,navi mumbai.
3. Symbiosis institute of design.
4. Unitedworld institute of design, gandhinagar.

After your BCA.

I hope it helps,

Best of luck.