The car, when new, is supplied with a separate cable (in a zip-up bag), which uses the same charging socket on the car as you use for your trickle charger (aka granny charger, because you use it when visiting granny). The end you plug into the car is known as a Type1 connector.
The other end of the cable has a Type2 connector, to fit the EV charging point, which can be something you have fitted at your home, or a charging point elsewhere. Some charging points have captive cables, but very few (if any) will have a Type1 connector on the end, which is why you would need this second cable. If you are new to the car, you may not have noticed the false floor in the boot, and it should be under that, together with a "can-of-goo" instead of a spare wheel. If you bought the car from a KIA dealer (or a seller who assured you that everything is there), I suggest you go back and ask for it.
You can buy a Type2 to Type1 adapter, for use with charging points with captive Type2 connectors.
The other socket on the car (next to the Type1) is a CHAdeMO socket. Some fast chargers found at (usually) pay-to-charge points use this socket. They have a captive charging cable, so you do not need a CHAdeMO cable in the boot. There is another type of fast charge connector, CCS, which I understand is not compatible with your SoulEV.
The differences between trickle charging, normal charging and fast charging are explained in the Owners Manual. If you did not get one with the car, see https://www.mykiasoulev.com/forum/viewtopic.php?f=2&t=1598