Feel the abalone slice with your fingers so you know how it feels before being tenderized. Pound the slice until tender. How will you know it's tender? The abalone flesh will feel noticeably softer when you touch it.
Some people use a meat tenderizer to beat the abalone into submission, but I've found many gentle taps all over the abalone slice with the back of a large spoon tenderizes the flesh without tearing it.