Hawking Radiation. There’s better explanations but the tldr of it is: particles pop in and out of existence all the time by “borrowing” power to pop in and giving it back when it pops out.
Every now and then, a pair of these pop in near a Black Hole. One of them falls into the Black Hole while the other shoots out taking a little bit of the Black Hole’s rotational energy and mass. And I mean minuscule.

Ordinarily this isn’t enough for a Black Hole to evaporate since it’ll consume WAY more matter than it evaporates. But as it stops consuming content, it’ll start -slowly- loss mass from Hawking Radiation.

This process is thought to happen faster as a Black Hole becomes smaller. It’s why massive Black Holes have an absurd theoretical lifespan like 10^100 years and small micro black holes live maybe like an octillionth of a nanosecond.

Btw I also neglected to mention the LHC likely would never be able to make black holes even if everything went perfect. Smallest theoretical Black Hole is a Planck Length wide (smallest unit) and the LHC slamming what they can into each other would make Black Holes about 10-15 orders of magnitude smaller than that…which isn’t possible.