The person who asks for support has not necessarily asked you to reclaim the job.

Wanting a hand and wanting to be relieved of something are two different requests. Someone who asks for help with a task they have taken on usually still wants it to be theirs; stepping in and finishing it removes the difficulty and the ownership together. What was meant as generosity arrives as a judgment about whether they were managing.

Before you take over, ask what kind of help is wanted: advice, an extra pair of hands, or someone to take it off them entirely. Then give that, and no more. If you find yourself doing it your way instead of theirs, stop and hand it back.