I'm sooo worried - enamel hypoplasia or hypomineralisation

OK so when my daughter (almost 15m) woke up I noticed this! At first she wouldn't let me see it clear and I thought a part of her teeth was missing, but now I got to see that it is a part of her enamel. Anyone dealt with this and their toddler? What can I do to make it better, besides goinng to the dentist as soon as possible. Anyone has more info why this happens in the first place? Could it be because of us using bottled water that is fluoridated?