Children’s voices in a choir sometimes have a sharp tone.
How can I adjust this in EQ with which frequency scheme?
You’ll just have to experiment with the Graphic EQ.
But I’m not sure how much it will help. It’s always going to sound like a children’s choir. 
You can’t create voices and voice ranges that aren’t there and it wouldn’t make much since to reduce the “children’s voice range”.
What is the format of presets in EQ? TXT or XML. Can’t find it. Whera are they located
Dynamic EQ , e.g. TDR Nova (free) plugin, on factory preset “de-ess (split)”.