how to handle legendary resistance?

[Henrique Oliveira Machado]

So, as title says. When we cast, lets say, a fireball into a dragon, the dragon rolls automatically the ST and fails.
How to turn that fail into a sucess without having to reroll again so the dragon takes half damage instead?

[Zacchaeus]

Untarget the dragon before rolling the damage dice and then roll the damage into chat. Then drag the damage from chat onto the Dragon's wounds.

[Henrique Oliveira Machado]

Untarget the dragon before rolling the damage dice and then roll the damage into chat. Then drag the damage from chat onto the Dragon's wounds.

cool, never thought on untargeting. Thanks