When you readjust to a new situation, usually one you have been in before, you adapt to it. I can understand why astronauts find it difficult to readjust to life on earth They are bound to take time to readjust after a holiday
If you readjust the level of something, your attitude to something, or the way you do something, you change it to make it more effective or appropriate. In the end you have to readjust your expectations
If you readjust something such as a piece of clothing or a mechanical device, you correct or alter its position or setting. Readjust your watch. You are now on Moscow time