In order to set a new date to the date picker you can use the .value() method, using an instance of the DatePicker. I can see that you are trying with:
Which is not a valid syntax, as you need to first get an instance of the DatePicker using something like:
datePicker = $(
and then use the .value() method to set the new value.
For your convenience here is a jsBin
example which demonstrates a possible implementation.
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