There is three types of restoring a backup. restore from the backups made with a plan, the backups saved in the datastores or the backups saved in the secondary server. Choose one of the options and go to next step.
In the next step, you should choose the source that you want restore a backup from and then choose the backup from the next step.
In the step number 4 you can change some restore options like if you want to power on the vm or delete the backup after restore.
And click the "Restore" button to begin the restore process.