Surge

You attempt to bolster a creature in the process of casting a spell. If the creature is casting a spell of 3rd level or lower, the spell is upcast as if the creature had used a spell slot one higher. If it is casting a spell of 4th level or higher, make an ability check using your spellcasting ability. The DC equals 10 + the spell's level. On a success, the spell is upcast as if the creature had used a spell slot one higher

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the spell Is automatically upcast as if the creature had used a spell slot one higher if its level is less than or equal to the level of the spell slot you used plus one.