I think you are thinking of the phrase  the other way around , which does essentially mean the opposite, but in a specific way. The specific nature of the other way around is that it means that doing what you say in the opposite direction is correct, not necessarily the exact opposite.
Once kittens reach 4 weeks of age, their mother usually begins to wean them off milk and onto solid foods. Because the weaning process can take up to six weeks, purchase a small amount of kitten milk replacement formula and mix it into your kitten's food during his first two weeks with you.
When the orphaned kittens are three to four weeks old, begin to offer milk replacer in a shallow bowl, then introduce a moist, easily chewable diet. You can make gruel from warmed milk replacer and a high-quality dry or canned kitten food. Serve it in a shallow bowl and feed the kittens several times each day. By five weeks old, they should be getting used to their new diet.