Yes - and the answer of "grind finer or increase dose" (as a way to address under-extraction) is dependent upon the coffee and the desired extraction / flavour profile.
To expand and clarify... the answer to the original question is "yes". You can, in theory, address under-extraction through either a larger dose or a finer grind (and in fact, through other methods as Jim indicates -- finer grind and lower dose for example). Which of these is optimal (rather than just possible), however, is a different question. It is, however, the only relevant question given that the answer to the plainly stated question ("which is possible") is useless ("yes" is not helpful).
Saying "oh updose" is also not helpful (the same is true of saying "grind finer of course") as this pre-supposes you know the coffee being used and the desired flavour profile and extraction (and potentially the machine and grinder being used). By saying, "grind finer, of course" what you would really be saying is, "on my machine with my coffee and to my taste I would grind finer". But the OP is not you, is not using your machine, and probably isn't using your coffee.
"Taste is the only morality." -- John Ruskin