In order to show different smartblocks to different users based on the device they are using, you will want to use the rule 'Current Device' which will allow you to select the preferred device to show the smartblock on.
To do this:
Go to 'Content' on the left
Select 'Slots' from the menu
Click on and 'edit' the slot you wish to make changes to
Select 'Rules' above the menu as in the picture below.
Expand the 'Person' field.
Include and configure 'Current device' within the slots ruleset.