So add Drow to the options for picking when creating a character it just says

Looking for something not in the list below? Unlock all official options in the Marketplace.

but I dont see a place or way to purchase to a single race.

In the menu at the top of any page click Marketplace.

In the submenu that opens click Store.

Click the book the race first appears in. (Drow appears in Player's Handbook)

Scroll down to the races or subraces. (Drow is a Subrace)

Click Add to Cart button next to the race/subrace.

Go to Checkout.

Add billing/payment details. Make payment.

Race unlocked.

Oh I have to know which source book it is found in, can't just search for drow.  But that works, thanks

Drow are PHB

What book are changelings

Quote from kierangggt >>

What book are changelings

 
Eberron: Rising from the Last War

I can’t find an add to cart button. I’m using the mobile app, do I need to be online with a larger screen?

You can’t purchase individual races through the app, you have to do it online. You can use your phone, just turn it sideways.