Filling Lookup Column via Nintex Workflow in the cloud

I am using Nintex in the cloud for SharePoint O365 in the cloud.

My problem is that I have a lookup field in a list linked on another list and I want to fill it using the workflow. OnPrem and in Designer this was done by entry [ID;#Text]. The ID was the found ID of the element in the source. I've now tried all possible combinations, searched half of the Internet and also looked up the field directly in the source, but I can't find a way to update this field in the element.
I very much hope that someone here can give me the decisive tip on what to do.