Second chance for legendaries? (Spoilers)

When I battled Giratina, I was having some trouble capturing it and I wanted to get one with a decent nature anyway, so I just killed it, thinking that I would get a second chance after the E4 or something. I haven’t yet been able to find a way to battle it again. I am now in the battle against Arceus and accidentally quicksaved right before the battle with a team that is not at all adequate for a battle to catch Arceus. Can I just kill Arceus and then come back to rematch it? Or is this the only chance?

I advice you to use a masterball on arceus in that conditions, I think you will NOT have more chances, so catch at least Arceus. I was in the same situation as you with Arceus and dropped a masterball haha

you dont have second chances to catch legendaries

perhaps only with Suicune, Raikou or Entei if you run from the encounter, but NOT sure