One week has past since I put the seed in the earth. I water the plant as soon as the earth feels dry (not completly dried out). I just use about 100-200ml water (because I don't want to "drown" her). My lamp is at 50% because it seems to be a little to intense for the small seedling at 100%.
UPDATE:
My first mistake
Found out that the leafs of my seedling rolled up, because the light was too intense for the young plant. So I put my light again on 25% (around 6.200 Lux). I have read that a seedling just can take light between 5.000 and 7.000 Lux. My lamp was around 18.000 to 19.000 lux! So I am very glat, that I haven't killed my plant 😅