This article explains how to unblock someone on Snapchat for iOS and Android devices.
How to Unblock People on Snapchat!
Because blocking people on Snapchat hides their accounts from you and yours from them, you can’t search for their names and then unblock them. Instead, you can access your list of blocked users through Snapchat’s settings. Here’s how.
Open Snapchat and tap your Bitmoji or username in the top left corner of the screen.
Tap the gear icon in the top right corner to go to Settings.