To enable planned start date first open More Service settings page, then click on Setup 

Here you can enable/disable planned start 

After changes are made, remember to click on update button

Planned start column can be shown in servicedesk overview, by enabling the column

After changes are made, you can then save the view so you dont have to do the same thing again. If you dont know how to save a view, click here.

You should be able to se planned start column in service desk overview now

To use planned start, create or open a case and add planned start date to the case.

If planned date exist on case, it will be shown in caseview

It is possible to filter, order and group on planned start date column.