The basic idea is that you don’t try to crack the slab’s surface but by pinching all 4 edges and bending them outwards so that the welded edges are “peeled off”. The difficulty between these approaches can be more significant on new slabs since the material is more flexible and easier to bend than to crack.
Here’s a YouTube video showing how to do it (you don’t need to understand the Japanese, just watch how they did it):
Tile nippers are recommended because ones without wheels are shaped like pinchers which make pinching edges easier.
