IPV4 option missing on Boot Menu for latitude 3190

I have Dell Latitude 3190 laptop. I plan to deploy using an IpV4 network boot. I have brought a LAN to USB adapter as these laptops do not have ethernet ports on them. I then went into the BIOS and enabled the network stack as I had been told too. The only issue is, Once enabling this and going back to the F12 boot up, it only shows Windows Boot Manager. It will not allow me to boot in any other mode. I have even enabled boot with USB and changed the fastboot options as was advised. I am stuck. I am not sure what to do.