Hi there Angel Noreen,
Welcome to planDisney and thank you for your question! It looks like your visit to the Disneyland Resort is just days away - how exciting!
A quick note that what was once called Disney Genie+ Service just got a name change to now be called
Lightning Lane Multi Pass. They function the same, but I'll refer to it as its new name in my answer so you know what to look for when you go to add it on.
With Lightning Lane Multi Pass, you can add it on to your tickets either at the time of ticket purchase or after you scan your ticket for the first time to enter a park during your visit. Since it sounds like you've already purchased your ticket, that means you'll want to add it on after you arrive and scan your tickets to enter a park.
My recommendation, and typically how I do it, is to have your
Disneyland Resort mobile app ready. Then after you scan your ticket and pass through the entry gate, you can navigate to the home screen of the mobile app and tap the "Purchase" button in the green Lightning Lane Multi Pass banner near the top of the screen.
This will walk you through a few steps to help complete your purchase and then you'll immediately be ready to go to use this convenient feature!
Thanks again for your question, Angel Noreen, I hope you have a wonderful time visiting the Happiest Place on Earth.
Have a Magical Day,
Greg