Populate Calendar If Date In Associated Cell Show Date On Calendar

I currently have a worksheet that when a user clicks on the cell, a calendar form opens. From here they can select a date, click ok, and the date gets placed in the corresponding cell they clicked on.

Now if the user needs to change that date, i want them to be able to click on the cell again, and when the calendar opens, the date in the cell would be selected on the calendar. I was able to do this in a userform, but im not sure how to edit it to work on the worksheet. I am using the below to populate the calendar.

Code:
private sub worksheet_selectionchange(byval target as range)
if not intersect(target,range("aa16:aa24")) is nothing then .show calendar
When the user clicks the date, the below code places it in the cell.

Code:
private sub ok_click()
with active cell
.value=calendar1.value
end with
unload me
end sub

Now the below code was used when I was using a userform, but im not sure how to edit this to pull the date from the active cell.

Code:
privatesub userform_activate()
me.calendar1=date
if not tb is nothing then
if isdate(tb.value)then me.calendar1.value = tb.value
end if
end sub