Have you looked closely for the block heater plug? Sometimes it's just hidden inside the bumper or under the hood.
If you don't have a block heater, it gets installed in the engine block. You need to remove the freeze plug which is installed in place of the block heater at the factory and install the block heater. If you are not familiar with working on cars it may be best to take it to a mechanic to have it done. It's a 1 hour job + the cost of the block heater, might be worth it to have someone else do it.
Here's the block heater you need -
Genuine Hyundai Engine Block Heater 3 3L 3 8L | eBay