Hi there.
We had a consultant do this bit for us. But I don't think it is very difficult and it is quite well documented.
You need an NDES server and you also need to install the Intune certificate connector on that server.
You need to create an appropriate certificate template on your internal CA server. You have to give "enrol" rights to the NDES server account.
Then you will need a certificate profile in Intune for handing certificates to Autopilot machines.
See more at these links:
https://oofhours.com/2020/04/05/intune-certificates-something-everyone-should-set-up/
https://docs.microsoft.com/en-us/mem/intune/protect/certificates-scep-configure
Cheers
Brian