First, remove the paper from the cans of condensed milk.
Place the cans in the Instant Pot or slow cooker.
Add water to the Instant Pot or slow cooker filling it up as much as possible without causing an overflow.
Place the top on your device and set it for 8 hours.
If using the Instant Pot, simply choose the slow cook setting and set the time to eight hours. If using a slow cooker, set it to cook on low for 8 hours.
After 8 hours, remove the cans from the device, dry them with a towel and allow them to cool.
Once they are warm to the touch, they can be opened.
Once the cans have been opened and the caramel has cooled, store the caramel in the refrigerator. The caramel can also be left in the can until your ready to use it as long as the can remains sealed.