This article describes how you can create the email with the trigger "x days before price adjustment".
Navigate to "Emails --> Emails"
Click on "Create Email"
Fill out the Create Email form
Fill out the Name field with something like "Price adjustment"
Select the wanted location
Choose x days before price adjustment at Triggered by field
Activate the Email dispatch
Fill out the Subject field with something like "Upcoming price adjustment"
Create the content to your branding and liking
Click on Save