Pretty sure its the one closer to the yellow transformer that is the cooler circuit relay. The circuits don't cross, so the heat relay is on the heat wire side, cooler wire on cooler relay side. But i think the blade terminals are labeled for the temperature, not the function (so hot is more like 'too hot, run cooler'). Could be wrong on the labels/wires, but whichever wire color goes to the compressor is the circuit you are after (originally, not after switching them!).
The good thing is it doesn't have to be that relay, just one that is the same footprint (common) and same or better ratings.
https://www.digikey.com/product-deta...1012-ND/280369
This should be equivalent.