Attaching directional antenna to dual-band mimo router

Good day,

I want to buy one or multiple directional antennae to improve the connection of my Netgear R7800 to a hot spot. The device has four antennae, and I am unsure which directional antenna to buy and what connector to attach it on. The four antennae are only labeled with 2x Antenna 1, Antenna 2 and Antenna 3 without any indication which frequency they operate with. What kind of directional antenna should I buy? Would a dual band one be the right choice? Is it important which connector of the router I attach it to? Should I buy an antenna that specifically supports MIMO? Any hints and tips a greatly appreciated.