Overtime is enabled via the standings configuration.

Either choose a standings template with overtime enabled – templates with 2pts win and Volleyball in the name have overtime enabled.

Or create your own custom standings configuration.

The standings configuration screen has this toggle to turn on the score inputs for overtime scores:

Once you have that enabled, you can assign points for OT losses/wins via the Scoring tab:

Please refer to the Standings help article for more detailed instructions.