How do I ask for an extension to revise a manuscript submitted to an Elsevier journal? I have submitted an article to an Elsevier journal and received the manuscript with reviewer comments and a "revision response due date" within the Elsevier evise system.

I am unable to meet that deadline and I need to ask for an extension. I assume it would be the most usual way to ask the editor, and I have done so about a week ago and not received an answer yet.

Now I wonder if there is any way to do this within evise. But if I click on "Agree to Revise" from what I understand I'm asked to submit the actual revised version already (see screenshot). I don't really dare to click the "Confirm" button to advance but may that be the way to ask for an extension also?

What would be the usual way to ask for an extension?
Write to the editor. This can be either via the system (see if they have a "send email" function) or simply reply to the decision letter email. It's likely the editor will say yes so you don't have to wait for a response to start revising your paper.

About the "agree to revise" button, clicking it tells the editor that you will be revising your paper after all. Some authors abandon their papers after a revise decision - I don't think they abandon the paper entirely, but they stop caring about the submission to this journal. It's good practice to remove these dormant papers from the system; otherwise it'll get cluttered. If you do not agree to revise, then after a reasonable length of time (several months, say) the desk editor might remove your submission. Since it's only been a week, you don't have to worry yet. There's no need to agree to revise for now: in the unlikely event the editor does not approve an extension, it's a (minor) administrative hassle to change the article's status again.