Assimilation is the change in pronunciation of a phoneme under the influence of its surrounding sounds.In other words, assimilation is the act of making two sounds in speech that are next to each other more similar to each other in certain ways, for example "eleven minutes"

After you have said "eleven", your tongue is behind upper front of teeth if you pronounce the /n/ sound, which is the wrong position from which to form the next sound, which is /m/.You get around this by changing the /n/ sound to /m/, like this: /ɪˈlevm ˈmɪnɪʔs/.You also replace the last /t/ sound for a glottal stop, which makes the word even easier to say

There are 2 ways of direction change: regressive assimilation and progressive assimilation.Regressive assimilation is the phenomenon in which the phoneme that comes first is affected by the one that comes after it.In contrast, progressive assimilation is the phenomenon in which the phoneme that comes first affects the one that comes after it