Most damage to flooded sergers or sewing machines is caused by rust. Even if the machine was not submerged, check for rust caused by general dampness. Rust develops quickly on highly polished, unpainted or plated surfaces.
Corrosion can ruin thread handling parts within a few days.
The serger or sewing machine head should be serviced by your local dealer within 10 days, if possible. Allow to dry naturally in a warm, dry place. Spray lightly on metal parts with WD-40 to prevent rusting. Do not get WD-40 on non metal parts or electrical components. Take to the dealer so they can disassemble the head.