Antennas in a Modem

I have opened up my modem and wanted to increase its range by adding better external antennas which it doesnt have. The modem has only internal antennas. I watched a video on youtube that I only need to unplug the cable or the piece that connects the antenna with the board but when I opened it up I noticed that piece and another piece that is melted on the board. I am not sure if I used the correct term here but as far as I know this is what I could say. I also did not know which one was 5g Wireless and 2.4 wireless but I did noticed that one of them is taller than the other. I tried to unplug it and turn the modem on to check which one and which but they both worked even one of the plugs of the antennas were unpluged. The correct piece hasnt arrived yet but I wanted to know what am I going to expect beforehand.