The Herta is a single stroke drag pattern made up of two 16th notes and two 8th notes. Instead of playing the “diddle” as RR or LL you would play it as RL, or LR.
Step 1: Imagine playing an eight note triplet pattern with the sticking RRL, RRL. Just like swiss triplets without the grace note (flam) at the beginning. Play with a legato stroke.
Step 2: Add the left hand in between the two right’s which makes it two sixteenth notes now and two eighth notes.
Play slowly with nice even legato strokes while increasing your tempo over time. Have fun!