nginx – How to make custom keys for DHE in TLS1.3

First things first, I am a newbie
In Nginx I want to use my own private keys (generate them using my own random number generator) in DHE to later use for AES encryption (as a part of the TLS1.3 handshake).
My question is how does one go about and doing this?
Is it in anyway possible to somehow this in the first place?
For context I’m using a FastAPI app

I’ve tried finding the answer on my own, but perhaps I wasn’t wording my problem right or I wasn’t looking hard enough, because I was unable to find an answer to this on the Internet.