When you are commissioning a new motor or swapping the current motor with another motor, you might get 'Position offset: No position offset existing drive error'. 

Double click the drive and go to Drive Manager tab, and select the 'Clear Error' from the Change Phase dropdown. 

Select the 'Position Offset 1' under Configuration->Motor and Feedback -> Feedback 1. Select 'No Position Offset' and click 'Activate'. 

Activate the Operation Mode phase. 

When the drive is in OP, now you can set the new position offset value and activate it. 

Save the project and activate the configuration. 

Now you can see the new offset value in the drive manager.