Simple and powerful! After that, when you get to a page where you'd like to fill out a form, the RoboForm browser extension or mobile app instantly fills it in. “Fill up” means to make something full, generally with a liquid. Form filling is easy! You just enter your information in RoboForm once. How does form filling work? As mentioned by the dictionary, it is often used to refer to a car’s fuel tank. 2. to become full So we see that “fill in” and “fill out” mean to complete a questionnaire, survey or form with the necessary information. (chiefly of a fuel tank) to make full.

I would say , “fill up” the application form because “fill in” means you need to fill something on a particular place, like for example we say:- 'Fill in th blanks', which means you need to fill in those particular blanks but in application forms the things are different. fill up - become full; "The pool slowly filled with water"; "The theater filled up slowly" fill change state , turn - undergo a transformation or a change of position or action; "We turned from Socialism to Capitalism"; "The people turned against the President when he stole the election" Fill up– 1.