Take the help from some of your senior/mentor. There is a standard formula using the values from standard and test (drug) sample, from which you can calculate drug concentration.

Some literature and links are provided for better understanding.

-https://www.researchgate.net/post/How_can_I_calculate_the_drug_concentration_from_a_HPLC_analysis_data_report

-https://www.researchgate.net/post/How_can_I_calculate_the_concentration_of_any_substance_from_HPLC_analysis

after plot A concentration vs time curve

Thanks Varun Ahuja and Sarhan Rashid Sarhan