If you wish, you register someone else to an opportunity head to the Opportunity Details page you are looking for and click on the Register your Colleague button.
The Register Volunteer window will appear,
Click and select the time slot.
Enter the email address of the person you would like to register.
Add in any other additional information required
Then click Confirm registration button.
You will return to the Opportunity Details page and find your colleagues' name in the Registration section.