Depending on how far into the game you are, this might not help at all, but it is best to perform void glitches as soon as you have access to the bike (you also will need escape ropes because you won’t be able to use fly). It usually takes less than an hour to get from the start of the game to this point. You want to be as close to the start of the game as possible so you don’t lose hours of gameplay if something goes wrong. If you do it this way, keep in mind that level 60 legendaries could be a pain to catch with weak Pokémon. This doesn’t actually lower the chances of the glitch going wrong, like the comment above says, but it’ll greatly reduce the consequences.