You can block or hide your friends by doing the following:
1. You can select the block/hide menu by swiping on the Friends list.
2. After selecting a friend from the Friends list, you can see the block/hide menu at the bottom of your friend's profile.
3. Tap on 'Message' tab> Swipe on 'Message' list and select the block/hide menu.
4. You can block your friends through the popup menu after clicking the '⋮' icon located on the right side in the chatroom.
You can unhide or unblock a friend by tapping on the 'Settings' icon at the top right of the 'Message' tab> tap on 'Hidden Friends' or 'Blocked Friends' and tap Unlock next to it.