The easiest is to just enter the date as text into the textbox associated with this input. Picking from a calendar is generally close-to-impossible but it is usually easily avoided. For instance just object clone the textbox and set text like "2019-01-07" with object cloning. Show some screenshot and code if you'd need more help.
u can try like this code:
step 1: chose any calendar
step 2: use Insert Keystrokes command with Currently Active Window then make code:
-> $input_year$[RIGHT ARROW]$input_month$[RIGHT ARROW]$input_day$
Hi failed to find the easy solution.. so had to choose difficult path. i spied on the first field and read the day. i found out which row or column does using the calculations and with the help of the index i choose the right row and column element. let me know if you still struggle i can send the screenshot