Need help in deciding an offer from Infosys

Hello, my friend is currently working in TCS as a QA Engineer with 4.5 YOE and 5.5 LPA CTC. Hello received an offer from Infosys who also has the same client with the same project.

Infy HR said that he'll be working for the same project and the team is also the same. Hello asked my friend for the expected CTC and he told 12LPA which he agreed immediately.

What is the fair CTC for my friend? How can he negotiate the CTC now since he already told the expected CTC?