I feel @Zardnaar
wants to reinforce that getting out of the Underdark is not a walk in the park. Like Boromir DoUrden once said: “one does not simply walk out of the Underdark”.
The Underdark is vast, unbelievably labyrinthine, full of monsters that want to eat you, full of plants that want to eat you, full of creatures that want to eat you, or at least eat your brain...That is without all the people who would take a shot at a lone drow, either by hatred, revenge, or just opportunity (including other drow). Not to mention the natural traps, chasm, treacherous terrain, etc. The Underdark wouldn’t supposed to be a super scary place otherwise. It may be beyond the abilities of a 1st level character without making it a campaign in itself.
Then, this implies that the drow character was either guided and escorted to the surface, or brought against their will. Magic shenanigans are also possible, as well as the “catastrophic results of a travel incident. Mercantile and surface raider background are the most obvious.
knowledge of the common tongue doesn’t have to be a result of the trip to the surface, it could also be the cause (character was sent along not because of their experience, but because their mastery of common, as an interpreter). Then there are 1001 ways of losing the PC along or abandoning them on the surface and as far as the PC is concerned, that is just fine.
there would also be 1001 reason for the PC to end up there against their knowledge or will, but then you need to account for the common language (assuming that the language is not relatively , well, common)