This should work in 2 ways.

1. sharing

Just customer can share details to any one. that details should contain App details and referal person details.

ig: Hey Buddy download Ultimate Grocery from app store and use my code 7ZBJK9ELIIGB7while sign up we both will get 100.0 wallet amount

2. Entering data in referal Screen

Customer needs to enter some details like name, mobile no, building no/area.