Hi Pooja,
To become a mentallist after 12th commerce you should go for B.A., B.A.(Hons), B.Sc., B.Sc.(Hons), B.Voc., Diploma, Dual Degree courses in Psychology.
Refer here for more info - Psychology Courses, Subjects, Colleges, Syllabus, Scope, Fees, Eligibility (careers360.com)
Feel free to ask doubts in the Comment Section.
I hope this information helps you.
Good Luck!
Regular exam updates, QnA, Predictors, College Applications & E-books now on your Mobile