To recover it (and all the items it contains), right-click the deleted folder, select Move, and then select a folder to move it to. If you delete a folder, it's moved to the Deleted Items folder and appears as a subfolder.

Tips for recovering items in your Deleted Items folder To restore a task, right-click it, then select Move to Tasks. To restore a calendar item, right-click it, then select Move to Calendar. To restore a contact, right-click it, then select Move to Contacts. Choose a folder location and then select Move. To restore a message to a different folder, right-click the message, then select Move > More. To restore a message to your inbox, right-click the message, then select Move > Inbox. To restore an email message, do one of the following: In your email folder list, select Deleted Items. Enter your user name and password, and then select Sign in. In a web browser, sign in to Outlook Web App using the URL provided by the person who manages email for your organization.

When you delete an email message, contact, calendar item, or task, it's moved to the Deleted Items folder.

Microsoft to do recover deleted tasks