Good sentence! I will make it a little clearer.
Correct sentence: Elephants use their trunks to smell, to pick up things, and even to act as snorkels when they swim.
Why this is better: each part uses the same kind of words (we start each action with "to"). That makes the sentence balanced and easier to understand. Another short way to say it is:
Elephants use their trunks to smell, pick up things, and even as snorkels when they swim.
Great job noticing what elephants can do!