maid of honor wearings backtracking to 1920

How did you mommys transition from formula to cow's milk? My baby finished her last can of formula today :/ shes 11m gonna be 12m on the 10th and idk how to do it she drinks alot of milk too.forgot to add that im using (infant & toddler transitions) 9-18m. maid of honor wearings backtracking to 1920