In order to change the owner of a locator, click on the checkbox to left of the locator key and click Change Owner icon. Upon clicking Change Owner link, a popup will appear that shows all of the users to whom you can assign the selected locator to. Once you select a user from the drop-down presented and confirm, that user will become the new owner of the locator. Only the owner of the locator and the Admin user can perform this operation.
You can alternatively get to the locator edit screen and then select a user from the Owner drop-down presented below and hit Save.