So PokeRNG gave you a seed to use but not a frame? That's very strange... If it does tell you a frame to use, then hitting the frame is pretty easy.
Let's say your frame is 19, as an example. Once you get in the game, you would call Elm 9 times to verify your seed, which would also advance the frames by 9. If you hit your seed, you would just call 9 more times (18 in total), then click on Zapdos, advancing it to frame 19, which would be your spread.