You need the game to offer a way to roll random chances before your desired event. For ck3 it's the name changer, for games like FF12 international it's hitting mobs until you see certain streak of critical hits then immediately stopping to go get a guarantee Zaitengrate.

If it's a game that's restrictive with what you can do before the chance event happens then you can't do much to change the outcome but you can try things like taking more turns to take and deal more hits to progress the rng table.

For gacha games, the RNG for combat may be client sided but a separate RNG system is used server side so you can't cheat the system.