How to connect a subwoofer to the sub-out output?

First, the subwoofer has to be self-powered, or you will need to add an amplifier for the subwoofer.

Our speakers has a dedicated subwoofer output port allowing you to connect a powered subwoofer, as long as the subwoofer can accept aux or RCA input. You are provided a 3.5mm-to-Dual-RCA audio cable with the set; the aux plug goes into the active speaker’s sub out port and the dual RCA plugs go into the subwoofer’s RCA input ports. If your subwoofer has a single RCA input port, simply use another audio cable that fits.

Our subwoofer T5 is designed to match all Edifier and Airpulse bookshelf speakers:

https://edifier-online.com/us/en/speakers/t5-edifier-powered-subwoofer