The 3102 used to be supported by 3CX, and at the time I had made a printout of the set-up page that they provided. I came across the printout recently. I had to scan it, then keep reducing the resolution to the point that it was small enough to upload. Some of the menu shots are getting hard to read. At least it this gives you a starting point.
Note that in step 16..... if your provider uses Bellcore type caller ID (North America, and some other areas), you will want to set the PSTN answer time to 3 seconds (not 0), or you will not "collect" the caller ID information, sent between the first and second ring.
And... as I said earlier, using a gateway remotely, unless on VPN (or perhaps, in this case with its own, static, public IP, not behind a router), is not supported, and will probably cause you issues.