In my first campaign as DM, I clearly stated in session 0 that we'd get to play in the Underdark. I explained the consequences very clearly in that the players wouldn't be able to see anything unless they had darkvision.
All the players took underdark-related races, but one player created a Firbolg character anyways, even acknowledging "then I'll be kind of blind 3/4 of the time, I'll roll with it".
In the session 1 I was kind and placed the players in a surface-friendly location where torches were lit in most places. We had quite fun when that character was forced to play blindly in less lit areas.
However in the long term that player will be handicapped by not seeing anything or by attracting many more enemies due to having a visible, warth-emitting torch. I don't really like that idea, but that's how D&D is designed, mostly.
The player is not really experienced but previously played two different campaigns which ran about 25 game sessions in total.
How should I deal with a player that intentionally hinders their character? They knew they would be blind most of the time so I think that my communication was clear enough. Usually, this is tackled in the famous session 0, which was done.
How should I have handled things if I actually already messed up?