Open the wish and tap Mark as fulfilled, or tap Fulfill on its card (first in the ⋯ menu on a phone).
There's no confirm step. Everyone who opens the list then sees a Fulfilled chip and a faded photo, and gifters see "[your name] already has this." instead of Reserve.
Marking a wish fulfilled also stops its price tracking, including Wishpicks Plus watching.
Steps
On a phone:
Open your list and tap the wish.
Tap Mark as fulfilled in the bar at the bottom.
Wrong wish? Tap Undo in "Your wish came true".
From the list, you can also tap ⋯ on the card and choose Fulfill, the first option. The ⋮ menu inside the wish doesn't have it.
On a computer:
Open your list and hover over the wish's card.
Click Fulfill, or open the wish and click Mark as fulfilled.
Wrong wish? Click Undo in "Your wish came true".
Can I undo it later?
Yes. Open the wish (it says "You marked this fulfilled.") and tap Put it back on the list, in the bar at the bottom on a phone. Or tap Activate on its card (in the ⋯ menu on a phone), which confirms with "[wish] is back on your list".
Free price tracking comes back by itself on wishes from partner shops while Price drop alerts is on. Wishpicks Plus watching doesn't, so tap Watch this price again.
Who can mark a wish as fulfilled?
You and anyone with Full Access can mark any wish, and a Contributor can mark the wishes they added. Gifters can't. You don't need to show what's reserved first, so marking a wish won't tell you whether someone reserved it.
How do I know if someone actually bought the gift?
You can't tell from Wishpicks: a reservation means someone plans to buy the gift, not that they have. A wish shows Fulfilled only when you or someone helping run the list marks it. You can check what's reserved, though: see "Can I see what's reserved on my list?".
Does it cancel the reservation?
No. The reservation stays and the gifter isn't told. They'll see the wish as Fulfilled on your list, and it stays in their Wishes → For others with a Fulfilled chip.
Tips
Got something on your list from outside Wishpicks, or bought it yourself? Mark it fulfilled anyway, so friends don't reserve it.
Sending the list round again for a new occasion? Mark what you've received first, so friends can see at a glance what you still want.
Tap Still open above your wishes to see only what you're still hoping for. The By fulfillment filter shows Fulfilled or Not Fulfilled wishes.