How to reduce number of trias in quads elements

Depending to your geometry. When you choose quad/quad only, Hypermesh already minimize the number of trias.

Sometimes, it's NOT possible to remove entirely trias. It's mathematical.

@Curro Capi de Camas

try with: 2D>elem cleanup>reduce tria elems

When active, this option attempts to combine trias into quads.  If you also enable elems failing QI check, the tria reduction will be tempered by the constraints on the resulting quads.