or ~to
If you work one substance into another or work it in, you add it to the other substance and mix the two together thoroughly.
Gradually pour the liquid into the flour, working it in carefully with a wooden spoon...
Work in the potato and milk until the mixture comes together...
Work the oil gradually into the yolks with a wooden spoon.
PHRASAL VERB: V n P, V P n (not pron), V n P n