To upload a backup file to a backup storage within Plesk:

Step 1: First, you need to log in to your Plesk control panel. Refer below link https://www.srilankahosting.lk/knowledgebase-new/getting-started-with-plesk/

Step 2: Go to Tools & Utilities -> Backup Manager

Step 3: Click Upload

Step 4: Click Browse and select the required backup file

Note: Make sure you select the appropriate backup file format, which depends on the operating system on which Plesk is installed. On Linux/Unix systems, you should upload tar or zipped tar archives, and on Windows, ZIP archives.

Step 5: Click Ok

Step 6: The backup file will be uploaded to the backup storage