Hi @allnull, welcome to the forum
This is explained in this post When parameterizing data, how do I not use the same data more than once in a test? and there is also some more discussion for a more … complicated scenario here Unique test data per VU without reserving data upfront, which currently isn’t as well supported.
You can also take a look at handling bigger data files which can be used to get the same effect(if you cut files in VUMAX pieces), but also having the benefit of potentially using less memory until https://github.com/loadimpact/k6/pull/1739 is merged.