Hi
Can you please supply us with a picture so we can see what you mean with 'keratin cyst'. It's not an expression I have come across so far in 15 years on this forum.
But soaking in warm water won't help with an swelling, whatever it is - a sebacious cyst, abscess, fatty lump (lipoma) or trichofolliculoma (a benign tumor at the roots of hair).