Where to Connect Output Converter for Subs, 2018 Nissan Sentra

I recently started hooking up my 1500 watt Planet Audio amp and 2 12in subs in my 18 Nissan Sentra SV. I previously had an 08 Dodge avenger with the same hook up in it. So with that pass knowledge I’ve already run the power cord through the car to the trunk and connected the negative/Positive cords from each subs to the amp. I will connect the ground wiring next but I am completely lost about where to connect my line output converter box. Please help.

Smart key? Regular key? Does it have a factory installed subwoofer? If so, Subwoofer (+/-)      yellow - blue (L); red - white (R)      +,-      amplifier under rear deck, brown 14 pin plug, pins 2 - 7; 10 - 9      

Left Front Speaker (+/-)      blue - pink      +,-      radio, white 20 pin plug, pins 2 - 3           Notes Right Front Speaker (+/-)      green - red      +,-      radio, white 20 pin plug, pins 11 - 12           Notes Left Rear Speaker (+/-)      lt. green - lt. blue or lt. green - violet      +,-      radio, white 20 pin plug, pins 4 - 5      

Not sure if it’s smart key or not and no it doesn’t have a factory subwoofer. I’m really a novice but I want to learn to be able mod my own vehicle.

Left Front Speaker (+/-)      blue - pink      +,-      radio, white 20 pin plug, pins 2 - 3           Notes Right Front Speaker (+/-)      green - red      +,-      radio, white 20 pin plug, pins 11 - 12           Notes Left Rear Speaker (+/-)      lt. green - lt. blue or lt. green - violet      +,-      radio, white 20 pin plug, pins 4 - 5           Notes Right Rear Speaker (+/-)      brown - yellow      +,-      radio, white 20 pin plug, pins 13 - 14