Default reviewer: define the default reviewer for an user when adding users to the Access Review. If the reviewer is available in the new copy/paste list or if the reviewer can be found from a previous review, then these are used. Only if the reviewer cannot be found for a user to be reviewed, then this setting is used.
Reviewer can review own account: Choose Yes, if the reviewer can Approve/Revoke own account. Choose No, if the reviewer cannot be same as the User being reviewed.