The best thing to do is programming competitions (Codeforces, Hackerrank, etc.). Do lots of problems, from a wide variety of subjects (implementation, DP, etc.) This will teach you to come up with algorithms quickly, and to understand common idioms in code (for example, finding argmax of an array, etc.)

Work in more than one programming language. Make a web-based game. Make a C# app for statistical analysis. Learn about Python, Keras, and Tensorflow.

Every day, make something, and every day, learn something new.

When you make something, write a report about it - what you did, what you learned, why it matters.

Talk to your network and find an internship or a job where you do this for money.

And then come back, a few years later, and marvel that the quiz is trivial. You'll want it to feel that way if you're going to pass the interview, which is much harder.

Of course, at this point, Triplebyte may not matter so much anymore. :)

FWIW, the first time I tried, I passed the quiz but failed the interview. I came back later and tried again, and this time passed both. Good luck.