If the question means changing identity of a specific user to some other value, it can be done either with an API call which updates a user property marked as "identity" or by using Backendless console. For the latter approach:
- login to Backendless console, select an app and click the Data icon.
- In the Users table, find the user for which you want to change the identity value.
- Once you find the user, click on the cell which contains the user identity value. It is going to be a cell at the intersection of the column highlighted with a blue color and the user's row.
- Enter the new value and press Enter to save it.
It might be possible that this question is about changing the identity property for all users. This can also be done in Backendless console:
- login to Backendless console, select an app and click the Users icon.
- Click the User Properties menu item. It will show a list of all user properties which make up a user entity for your application.
- A property which is marked as "identity" has a radio button selected in the identity column.
- Click the radio button for the property which should become identity. It is important that all existing user objects contain a unique value for the new property, otherwise, Backendless will not be able to accept the selection.