The first step is to determine if the FD itself is causing the chain to fall off. If the outer plate of the FD is touching the chain when on the granny and inner half of the cassette, then you have an FD adjustment issue, most likely the inner limit screw. It could also be a trim issue (cable length adjustment) if the shifting and trim on other chainrings isn't spot on.

If the FD isn't touching the chain, and the only way to prevent it from coming off to the inside is to have the FD keep it on with the inner cage plate, then you have a sprocket problem, most likely a single bend or dinged tooth.

Either way the first step is to determine why the chain is coming off, and pinning it either on the FD or the sprocket engagement. It's also possible that a damaged link in the chain itself is part of the problem, but this is comparatively rare, and my money is on the FD trim.