Fair market value of a share allotted by IIFL Wealth management in September 2018

I purchased shares of IIFL Holding in October 2017 and the company, after de-merging  allotted shares of newly created companies IIFL  Finance, IIFL Securities and IIFL Wealth Management  sometime in 2018 after 31-01-2018. I sold some shares of  IIFL Wealth after it was listed in 2019. So for the purpose of LTCG calculation how do I find the Fair Market Value ?