Please go to:
Overview => Data Import and Export => Export Data
Scroll down to the section "Export Submission and Review Information, Reviewers and Session Details" and please select "Export of Reviews" and additionally the option "Include open (newly assigned) and draft (incomplete) reviews".
Scroll down to the bottom of the page, choose an "Export Format" and click on "Create Export File"
You will then get a list of submissions that includes review assignments and reviews.