1991 Mazda on the emission test failed on the NO (PPM)

Question

Smog test results for my 1991 Mazda on the emission test failed on the NO (PPM) it read
15 mph max 815 measured 1117. At 25 mph max 536 measured 786. I was told my car is running a little hotter than it should. What do I need to fix so it will pass smog? It passed all other tests for smog. My check engine light does not come on. Thank you, Sandy Roberts