For starters, if you are using a 3rd party control you should at least tell us who makes the control so that there is a proper point of reference.
It turns out you are using the GrayMatter Software Date Picker control.
When you initialize the control you just need to set the date.
<cc1:gmdatepicker ...="" date="<%Put Your value here%>" xmlns:cc1="#unknown"> ... </cc1:gmdatepicker>