In Donedesk, use the Soft Date to mark something as Someday/Maybe. Choose “Someday” from the list of options.
Note: This option only appears if you have Donedesk configured correctly for TRO. If you skipped a step when setting up your tools, you will see a calendar instead. To change this, click your face at upper right, choose Preferences, and uncheck Select Soft Dates From Calendar.