Refer the following article to know How to create a Register Automation / Register Rule?
In order to apply the Register Automation, you must edit the register. Follow the below steps to edit the register and assign the Register Automation
1. Click Settings on the Navigation bar and select Stores & Registers from the drop-down
2. Click on edit to make any necessary changes
3. Scroll to the Register Rules field, select the created register automation and click on Edit Register to save the changes made