My 93 mazda protege failed emissions due to oxides of nitrogen(NOX), how do i fix this?

It could be the catalytic converter but the place to start is the EGR valve and passages. Exhaust Gas Recirculation is how the engine cuts down on NOx production, while the catalytic converter works to break the NOx down. The usual problem is that the EGR valve and passages become choked with carbon. I'm not familiar with how to clean the passages in your Mazda but any experienced mechanic should be able to do it affordably.