Your employee can change the amount they receive for each FBP component as long as you have the FBP Declaration window released.
To release FBP declaration for your organization
Navigate to Settings → Tax and Statutory Compliance → FBP Declaration.
Click the Release FBP declaration button and set the Lock Date in the field Allow employees to submit FBP Declaration until.This defines the last date for employees to submit their FBP Declaration.
For new employees, enable and configure the number of days (from the date of joining) during which they are allowed to submit their FBP declaration.
Click Save to apply the settings.
By default: The FBP Declaration Lock Date is set to 30th April of every year and For new employees, the declaration window is 60 days from the date of joining.
Fig: FBP Settings