You didn’t type up any text with your post, which is usually pretty important to do to explain your issue.
But luckily, I knew what you meant.
You can’t successfully trigger an automation based on the contents of a field changing, so you would have to do it in a different way.
The current best practice is to create a single-select field that has a drop-down option in it entitled “Send Email” or something like that.
Then, change your automation to trigger when the field matches “Send Email”.
At the end of your automation, you can then change the single-select value to a different value, clear it out, or leave it as is.