Dear Aspirant, I am stating you the steps to Challenge JEE Advanced Answer Key. The steps are:-

1. Visit the JEE Advanced official website.
2. Open the candidate portal.
3. Login using JEE Advanced application number and password..
4. Click on the link to challenge answer key.
5. Mark the number of question whose answer is to be challenged.
6. Upload the documents in support of such objection and pay fees(if applicable).
7. Click on submit button to challenge.

I hope you are clear now. If you have any other queries feel free to ask. All The Best!!!