I actually got this in the first battle of the campaign, but it will probably get easier later in the campaign with deck upgrades.
First you need to make sure you have some creatures in the graveyard before you use a card to return it to your hand.
I used the Gravedigger creature card which returns a creature from the graveyard to your hand when it enters the battlefield and the Cruel Revival instant that destroys a target non-zombie creature and lets you return a zombie from your graveyard to your hand.