Can you possible post some screenshots and give us a rundown step-by-step of your workflow? Here's some information I've found on editing these domains:
https://doc.arcgis.com/en/arcgis-online/manage-data/define-attribute-lists-and-ranges.htm
Here's a screenshot of one of mine:
You'd need to go to your feature layer, data, fields, and then find the field and domain.
Cody