Application is a document editor with the ability to add text, images, blocks, and fields. Users can assign fields to recipients and send a document. I'm currently working on an interface where users can set up conditional logic for fields in a document. Users will be able to set up a logic where for instance there is a dropdown and if a recipient selects "option 1" then some fields appear in a document. The conditional rule configurator looks like this: it's a separate mode. On a screen, we have a document itself and on the right side, we have sections: trigger and condition 1 (we can add more). In condition 1 we have IF and THEN parts. So in THEN part users need to select which fields will be shown when a particular value in a dropdown will be selected. Once they click the "Select fields" button then selecting fields mode is enabled and users can select fields from the content in a document (it's much easier than showing them all fields in a dropdown with their IDs). Selected fields change their style and become striped and they are added to the THEN part in the right panel.
My question is: how to attract users' attention to the content part and show that it's time to select fields and then direct them to finish the selection when they are ready? Taking into account that there are many fields that could be in a document and also fields could be above/below a scroll.