You can try ans give motivation, offer emotional support, sometimes even offer to do the thing together (sometimes just arranging a thing is a good way to not let it slide), but forcing will have the opposite effect and will only add to the internal pressure that is already there (but you won't probably see) and that is not enough. Of course it depends on the person, you can also ask your friend, as long as you accept the answer as a fact with no judgement (it's not easy but probably it will be appreciated)