I remember starting it a few years ago, but seem to have lost it while switching apps and can't seem to find it in the time travel category.

The premise is that a middle/high school boy was walking home with his crush and she ended up being killed by a truck. He falls into a lake and finds out that he travelled back to the morning of the incident. He redoes the day multiple times to try and save this girl, eventually succeeding. He then uses this power to help other people, though he must relive everything from the same morning where the girl was hit by the truck.

Saike Mata Shite mo? Tried searching for "Time Loop"...

~4400 manga completed
~1700 ongoing...

You got it, thank you!