There are plenty of resources on how anyone can learn mentalism tricks and become a mentalist. The first thing you will need is a solid foundation.
There are lots of good books on the foundation of mentalism that you can find all around you. Instead of focusing on specific tricks, you will want to learn how to present them. Without this skill, you will find it really hard to make people follow you.
It’s just a trick after all just like magic and others. If you are too serious about it and just want to learn these tricks then the Internet is your friend. You can find hundreds of tricks for free online like this course. You just have to look hard enough.
You may want to give preference to video tutorials as these are just so much easier to follow than a text. When looking for a reliable source of detailed tutorials and explanations of various tricks that mentalists use together with the skills needed, you will need to find a book that covers all of the basic stuff but most importantly an incredible amount of magic and card tricks.
When you are learning card tricks, just always keep a deck with you. You will find plenty of time to practice throughout the day then practice with an audience like friends and family. When you feel confident enough, practice the tricks with strangers. This will be the ultimate test to your skill and finally something a lot of people tend to not do is connect with others. You will learn a lot from others and get motivation to help if you need it. I think this is super important. It’s really simple, learn the basics of showmanship to actually wow your audience, learn some tricks and practice practice and practice!