It is quite common to describe life as a story. As such, we often think of aspects of our lives as chapters. This is totally cool. Certain events or challenges mark a period of time with an overarching theme. When we complete a task or reach a new understanding, that arc has finished and the next one begins.
But as great of an analogy as that is, it actually does not hold up as much in writing. Until a book is published, you can always go back to previous chapters. You can always change things from a slight tweak to a major shift.
To a degree, though, we usually do not want to make a change that is so big that you then have to rewrite everything that follows it (and some things that precede it, too). However, you do have the option if you want it.
You may have written the chapter and moved on to the next one. You may feel like it's now set in stone. But ask yourself: Is that chapter behind you?