Covidence doesn't encourage the specific dividing of records for screening. There is no mechanism to have a particular reviewer (or pair of reviewers) screen a particular subset of the studies in a review. Covidence is designed in this way to minimise the bias in voting patterns that could result from this type of allocation.
To ensure that the screening work in your review is divided up equally, we generally recommend asking each reviewer to track their overall contribution from the Team settings page, and to 'aim' for a particular number of votes contributed. You'll still end up dividing the work fairly evenly, but this minimises the risk that one segment receives an overall different assessment than another segment.