PiVPN with 4G/LTE Hat V2 EC25

Dear all,
I am a beginner in this domain. I am trying to create a PiVPN with Sixfab 4G/LTE Hat and Quectel EC25 shield. For that, I need to do some network configuration. Like, fix the IP address, port forwarding etc.
I got the HAT working with ECM interface. Please guide me about this.
Thanks in Advance