JMeter: How to send HTTP requests with different request body for each thread count?

JMeter: How to send HTTP requests with different request body for each
thread count?

I am testing a REST API that creates a user. This API uses POST method and
requires a json payload. I am using the HTTP Request Sampler for my
requests which accepts a file for the request payload. The issue I'm
having is that the request returns a 409 Conflict for all the hits except
for the first thread because after the first thread is executed, the user
already exists. Is there a way I can tell JMeter to pick a different
payload before each request? How can I organize my request payload for
this purpose?