Hi Praveen,
The requirement you have mentioned 'Minimizing all TileItems' can be achieved by clicking on the minimize button on the top right corner of the maximized tile.
If this is not your requirement please provide us more information on your requirement whether you need all the TileItems to be minimized through a button click.
Please provide us snapshot of your requirement,which will be helpful for us to provide you more accurate solution.
Please let us know if you have any queries.
Regards,
Vignesh V