Welcome!
What you do with the Scalecoat Wash Away is pour it in a jar of suitable shape then soak object for a while - I haven't looked at directions for years but they did say something like soak for 15 to 20 minutes, and rinse off while scrubbing with old soft toothbrush. I usually hit it with brush before removing from jar or while removing, so the sludge gets captured in jar.
Liquid is reusable and will last some time.
Photo is of styrene body of old 1970s HO scale locomotive which was given to our club to see what we could do with it, if anything. Factory paint of Sylvan Green had been painted over with grey and red of what looked like paint by number oils practically troweled on. I let the thing soak for about an hour, twice, and am at this point.
Note that factory stamped lettering and trim remains, that's a common quirk; there's no telling what's going to take off just the lettering, just the paint, or both, or nothing - is frequent conversation about that on model train forums.
Oh, I don''t remember if anybody said in thread but high percentage isopropyl alcohol, aka rubbing alcohol, will sometimes work as a paint remover and I've not observed it to damage plastic models.