This is a simple one.
If you’re using the website: login, then go to your own profile. You’ll see an option in the left column to view Blocked Members. In the pop-up, select whom you’d like to unblock.
If you’re using the new Grokio Communities app: tap on “Me” in the bottom right corner, then click on “Blocked Users” in the Account section.
If you’re using the old app: tap on Browse, then tap Blocked Members.
Keep in mind that once you block someone, there’s a 72-hour waiting period before you can unblock them (this is to prevent abuse of the block feature).
Hope this helps,
The Grokio Team