Probably best to buy a second panel with controller and run both sets of wires to the battery.
Otherwise you'll need to access the controller input wires to connect the second panel. Panels should be identical and the controller has to be spec'd for 2 panels and you may void any warranty.
Very common to connect panels in parallel, series or series parallel with 2 wires going to an appropiate controller.
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland
Bob