Rotten soffit

hi everyone

So it's just one end of the board that's rotten.

I've faced rotten facia before but not the soffit and I'm just wondering what's the best way of going about it?

I thought cut out the section with my multi tool and put a new bit of wood in but I have no idea where I would fix it... cutting/drilling a hole for the vent should be fine it's just fixing a new piece I'm concerned about. Or is there more to be concerned about?

Any ideas would be greatly appreciated!