Follow these steps to setup a loyalty activity that can reward your members additional points for a limited period of time:
Go to setup a New Loyalty Activity
Make sure it's a single step activity (this doesn't currently work for multi-step activities)
Set your points, date parameters, etc. and then enter the multiplier in the Enter Reward Amount: section. If you want to give them double points, enter 2.
If this is only for a specific location, make sure that you set the location under Advanced Options.
On the next step, assign the activity to "Commerce Order Placed" and continue.
If you weren't prompted to connect to an action, click on assign new action.
Please note, when you issue double points (or higher than 1 multiplier), the system will not process the users' loyalty rank multiplier.