I would buy amine reactive HRP from Thermoscientific and follow their protocol for the kit. I would prepare my own solutions: 5M sodium cyano borohydride, 3M ethnol amine, pH9.4 and carbonate/bicarbonate buffer pH9.4. You will need to desalt the antibody wih a spin column if it contains Tris buffer and or sodium azide, or any buffer that has amine reactive groups. Basically, you reconstitute 1mg of amine reactive HRP with 100ul of ultra pure water. Then you add 1mg of antibody, preferably, in the bicarbonate buffer, 0.5-1ml. Let react for 1hr. Then in a fume hood, add 10ul of the sodium cyano borohydride to reduce the Schiff bases that have formed. After 15 min, add 20ul of the quenching buffer which is the ethanol amine solution. Then you can desalt the conjugate by dialysis or another desalting spin column. Store conjugate at 4°C for up to 4 weeks.

Ohhh! It is fine! Did conjugation work well? I need too.