You can not change your post date on Instagram. In the edit post option, you can change post caption, image Alt text or you can tag people.
When you upload content for an Instagram post, your post publish date time is taken automatically. And, this date is shown at the bottom of your post.
Here, to change the date and set the current date, you can create a new same post again.
But, if you want to edit an Instagram post upload date and want to set a specific date, then no such option available for that.