Learn to clear iPhone data by deleting local backups
Open Settings and tap on your name or profile picture
Tap on “iCloud”
From the directed page, click on “Manage Account Storage”
Tap “Backups”

Choose the device
A list of all local backups for your iPhone will appear. Select the backup you want to delete and click on “Turn Off and Delete from iCloud”

Know more: https://techybrain.net/how-to-clear-system-data-on-iphone/