How can I use my small flashlight as my bicycle's headlight? How safely add my small flashlight to my foldable bicycle temporarily? I want use it as headlight. But I need take it off when I don't bike.  My folding bicycle doesn't have basket, and I don't want add basket.
Because COVID19, I don't want spend money buying light. My small flashlight has a handle.Let me know if you want me write out flashlight name and model.
Michael wrote below

In any case, please make sure to mount it in a way which doesn’t dazzle oncoming traffic.

Criggie

I'd suggest angling this down at the road more than forward.

OK! I know. You can adjust lumens, and I use just 80 lms in day and 800 lms at night.
Can you maybe use zip ties to mount the handle to the stem, then attach the flashlight to the handle when needed? Can be tricky to get the angle right.
There are also universal flash light mounts, though I’m not sure they’ll work for the rather large diameter of yours.
In any case, please make sure to mount it in a way which doesn’t dazzle oncoming traffic.