Like Bob said, if you do a surface patch it will crack again in no time. It looks like the footing settled, maybe because of that dirt against the wall got saturated with water and when frost hit it caused the damage,etc.
So you basically have 2 options, do this the right way, or do a band-aid job which will not do you any good and you will be called back each time the crack reappears.
Right way to fix that, is using foundation epoxy injection method and Carbon-Fiber staples, which called stitching method... but before that, that retaining wall will have to be removed, because if you repair that small portion it will not do you any good, because the water will continue to penetrate the wall cavity bellow behind that retaining wall and each time the frost hit, foundation crack will change its direction and reappear.
Good luck