Hi @Florian,
You’re not doing it correctly - this updates a single record, and you need to know its ID 
You need to set up something like 3-step flow in Integromat: GET ALL → Iterator → Update.
Some time ago I was experimenting with mass update via Intergomat, this is an unlisted video on YouTube which you might find useful: Adalo experiments: mass update via integromat photos and categories - YouTube
Of course you don’t need to replicate everything there - this is just for the reference how the things could be set up.
Not a basic question, btw 
Best regards, Victor.