There are two types of backups:

1- Full Backup : Copies the entire compute volume.

2- Incremental Backup : Copies only the changes made since the last backup.

In the Manage Volumes window, select the volumes you want to include in the backup plan.
Click Save.

Retention: 7 Days – Creates a daily backup of the selected volumes and keeps up to 7 full backup chains. In this case, the max number of recovery point is 1.
Retention: 14 Days – Creates a daily backup of the selected volumes and keeps up to 14 full backup chains. In this case, the max number of recovery point is 2.
Custom Retention – Allows you to set a custom backup schedule. You can choose specific months, days of the week, days of the month, backup time, and the maximum number of full recovery points to keep.

Uncheck the volumes you want to remove.
To filter and view only assigned volumes, check Show Only Selected Items near the search bar.