I'm wondering why you did not google before asking this question. In addition, your question is not well formulated. The reaction rate constant of catalase with H2O2 can't be CALCULATED, but it can be determined (measured) experimentally. How? Google will help you.
In addition to what Yuri Geletii wrote, the rate constant is known. It was determined in the late 1940s. It was possible thanks to a new instrument, the stopped-flow spectrophotometer. Now, you have enough hints!
There is no substitute for reading the literature, googling will not do it. And if you read these old papers, you will also find out how to calculate the rate constant.
If you have your data as a function of time, there is a powerful software called Graphpad prism "https://www.graphpad.com/", by which you can fit your data in double exponential decay from the options of different fitting equations, as a result you will get the first and second rate constants.