Both MPPTs go to the batteries, or to your battery bus.
See here in these picture below.
In the centre bottom you will see that I have a negative and positive bus. Of the 3 cables for each, the left most set (+ and -) go to the battery. The centre set (+ and -) go to the one MPPT and the right most set (+ and -) got the the other MPPT.
If your current MPPT connect to the battery terminals of the Inverter, then both can connect there. I find that things get a bit tight, so mine goes to the battery (actually to the fused port(s) of the battery) and the battery has it’s own big thick cable to the inverter.