You asked, and we listened!
One of the top requests from the ArcGIS Online user community is to support bulk attribute updating.
We are excited to announce that selecting and updating the attributes of multiple features is now available at this update of ArcGIS Online!

You will be able to open the Attribute pane with multiple features selected to view and edit their attributes. Either enter in values to overwrite all the matching fields in your selection, or browse through the carousel of features to make individual changes.
More resources
To learn more about ArcGIS Web Editor, check out the resources below:
Be sure also to check out the NEW VIDEO – An Introduction to Web Editor
Hi Martin, this is a great addition to the web editor app but are there any plans to change the licence requirements for web editor? This is also one of the most requested features as per this ideas post. As it stands web editor is not available to a large number of users who have editing capabilities under their licence and this means those that are most likely to use it (i.e. those that don’t have ArcGIS Pro) cannot access it. It would be great if the team could reconsider this restriction as web editor is something we would likely… Read more »
Totally echo what Anthony says. Bulk attribution is great, but the request to reconsider the licencing restrictions, and make this available for mobile workers has 3 times the number of upvotes and is just being conveniently ignored
100% this.