6th Gen How do I get back to Primal Groudon and how do I catch it?

[Venonat in Space]

I had to use an escape rope cause...I don't know, I have my reasons. Also when I previously tried to catch Primal Groudon, he ran out of moves and used struggle, then went down to 1 hp. Still no luck in an ultra ball. I know I don't want to use my master ball because I have to save it for Rayquaza or someone else post game. Now I can't get back to primal Groudon cause I escaped the cave previously. Help?!?!?!?!?! A PM or response will do. Thank you in advance.

 

[PKMN Trainer Jorvyn]

Did you go back to the Cave of Origin? If you've fainted him, you have to beat the Elite Four for him to reappear.

Also, don't use your master ball on Rayquaza, he has an extremely high catch rate for that battle. I caught mine in a regular Poke Ball.

 

[Venonat in Space]

I found Groudon....somehow out of sheer luck. xD But I still can't catch him x(

EDIT THE NEXT DAY: Eh...I sort of caught it in a Master Ball out of total frustration, then did a wonder trade with another Pokemon and whoops! The game saved. I dun goofed so feel free to lock this topic. I apologize.