JavaScript is not getting loaded

Just a newbiw I am trying to make a bookmarket for a specific page where some Combo/Select box exist

i am trying to auto select required values in the boxes through bookmarklet.

however Input id exist on the page but while testing in the console it is showing null and after some time (no time limit-sometimes it is getting one hour) i am getting the whole element.

Screenshot

as a newbie i have no idea... please help... it will save my hours in my daily working.. i will make the bookmarklet auto run with tampermonkey