Hi sfcurley,
You can uncomplete a task from any of the apps, but generally you can find an uncomplete "left + up arrow" button at the top. (This is above the task list in the web/desktop app and above the task details in the mobile apps.)

Also in the mobile apps you can swipe right on a task's row to uncomplete it (and you'll see the same arrow as you do so).

Generally the uncomplete action is the same as the complete action, just depending on which task you select.)

Hope this helps but let me know if you need any further help!

This is very odd.
I can't find any un-complete action on the web (Firefox 89.0 Linux) either.
And it seems to have disappeared from the android app (4.5.12).
I thought there might be a workaround to 'Add field' but 'completed' isn't available.
All very odd.

What I would like under RTM is to be able to complete a task and have it transferred to a journal. I thought I could emulate this by moving 'completed' items to an 'archive' list but this doesn't really do what I want, as for repeated tasks it moves future tasks to the archive.
Unless the wisdom of the crowd knows better ?

OK - I spotted an "undo last action dropdown on the '...' box on the web version.
And a ⤺ undo button on the (android) phone app.
That's nice. Really but not an uncomplete facility,

General feedback: the uncomplete button is not in an intuitive place. I might suggest putting it somewhere more prominently.

I can't find it either :)

I mistakenly mark a task as complete and it's been frustrating to figure how to undo that. I end up deleting the task and recreating. RTM help documentation didn't help much. Reading the comments on this post, hopefully I'll find an easier method to address the next time it happens.

I usually use the web version for task management and I, too, have trouble remembering what to do if I complete a task by mistake. I couldn't really figure it out by reading these comments, either, but knowing that such a feature did exist, I found the rounded arrow that points to the left. To me, that looks like a "go back" button, so I wouldn't have thought to try that.

One thing that would be helpful is to put the "how to make a task incomplete" information in a help topic.

Great tip mmoore! I too would never expect the curved arrow to reverse an item that I mistakenly marked as, "complete." Yes, it looks like a "go back" button. I mistakenly looked at the "Completed" tab, clicked the item and then "Incomplete" at the top right, thinking it would put it back on the "Incomplete" list.

I've also wanted an uncomplete keyboard shortcut for the web for years.

My use case is my shopping list. I reuse the completed items over and over. I mark "milk" as uncomplete when I need some. That's faster than creating a new task, and your completed shopping items serve as reminders when prepping a new list.

I'd suggest the character `c' so it works as a toggle.