Only the review owner (whomever set up the review) can invite other reviewers.
To invite other reviewers to your team, select the review you are working on, and press the 'invite' icon.
A pop up box will populate. Type the email addresses of everyone you wish to invite and select what level you would like them to be set as.
A collaborator can do everything on the review except delete it, invite others, change the blind status, or delete search methods not created by him/her.