All designated reviewers will get an invitation Email. An ISHS membership is not required but reviewers have to sign in. It seems that by invitation of yet unlisted reviewers (those without any ISHS account and membership) a preliminary ISHS account will be created automatically for you. Please check.
Please see the manual for an in-depth discussion of the review process: ISHS online submission and review tool guidelines for reviewers
Use MS Word and make your assessment with inserted comments and using the „keep track of changes“ feature.