Hi @PRACHI_GUPTA,
Welcome to the Bunnings Workshop community, it is wonderful to have you with us.
This kind of question comes up pretty regularly. My colleague has provided a good explanation of how to add shelving to existing cupboards in the discussion How to add shelves to cupboard?
Essentially, you would add cleats along the three available walls of the cupboard, screwed to the framing, which your shelf will then sit on and attach to.
For your cleats, you can use something like this https://www.bunnings.com.au/66-x-18mm-5-4m-white-moulding-pine-fj-primed-dar_p0020750 , and for the shelf, you can use chipboard to match the existing shelf.
This approach will work in almost all cupboards, however if you have any particular questions or concerns about the process, please let me know so I can assist further.
Jacob
