PCI device in linux

So I am working with a super duper intercom system running Linux. Long story short we had to replace the motherboard, which invalidated all off the licences and the system is no longer running until they send me updated licences, to do that they need the MAC address. These are the instructions they sent me.

Open The terminal windows,
Enter “vim /etc/udev/rules.d/70-persistent-net.rules” then hit enter,
Move the cursor down to the line #PCI device xxxxxxxxxxxxxxxx then hit keyboard ddddddd… until all gone.

Hit “Esc” then “wq” hit enter again. *wq=write and quit
Your networking will be running again after reboot panel.

Find out the mac address on mother board networking port by typing “ifconfig” command.
I can create new mesh license for you. Ok

After doing this for an hour and a half (and going crazy because it wouldn't work) I was told to use sudo.

I am not to familiar with Linux and found a lot of info on google but have no idea where to start.
Any help would be awesome...