I am trying to find the principle of moment of inertia in round house kick. Can someone help me explain using the calculus.

What particular physical aspect of the round house kick do you want to understand by means of the moment of inertia?

If you want to totally understand the theory of the moment of inertia, you need some integral calculus (although you can do without much) and some vector algebra (perhaps a bit more than calculus.) But qualitative discussion of some simple cases can be done without big mathematical hurdles.

You don't need Calculus.  Just basic math skills can solve the problem.  You must like MuayThai so much, right?  lol.

Reference:
How to calculate Moment of Inertia? - Formulas and Solved Examples – https://www.geeksforgeeks.org/how-to-calculate-moment-of-inertia/