The Sync with Master dialog allows you to re-establish connections between the master and alternate layouts.

Access this dialog by clicking Sync with Master on the selected object's Advanced Properties dialog.

This dialog includes the following options:

List A tabular list of all the attribute discrepancies between the master layout and the alternate layout for the selected object.
Master Updates to Alternate Value Select this option to have the master layout adopt the attributes of the alternate layout.
Alternate Reverts to Master Value Select this option to have the alternate layout adopt the attributes of the master layout.

For more information, see Create an Alternate Layout