Hopefully you figured this out as a long time has passed on this thread without any response but I'll leave a note for others that struggle.
Date pickers can be among the hardest UI elements to interact with during RPA development. I suspect the exercise here is not to try to set the date using a write stage - the date in the date picker does not look like an editable field. The real world type exercise here is to navigate the data picker using the mouse. Navigate to the right month, mouse click on the right day.
In the real world you would create a reusable object called something like "Citrix App Date Picker" with an input of the date and the action would:
* Read current month & year
* Use left and right arrow buttons with global clicks to navigate to the correct month and year you want to enter (probably a loop that keeps clicking, waits for month text to change, and then compares month text with month you want)
* Global click on day you want
