I have turbotax online assist & review self employed for 2024. I have used it for myself & partner. My son will be filing taxes this year (18). How can I add a return

Since your son is under 25, he qualifies for "25 or Younger" promotion. If he has a simple situation, he can file for free or he can use Assist and Review for $20. Visit https://turbotax.intuit.ca/tax/offer/25-and-under for more information.