connecting security dvr to 5G modem

I am attempting to hook up my DVR (security) to our 5G modem (LRV5-92-D4). I have lights at the

RJ45 jack at the modem and the light showing network is on on the DVR. However I cannot get the DVR to connect to internet. I have attempted to set the port forwarding but still have nothing. I have even changed the cable to a different RJ45 on the modem with the same results. Can anyone give me a little guidance. I'm an old man and not too smart with all this tech. Thanks in advance Daniel