At this time, you can't merge your Pinterest accounts. If you have more than one account you can either keep both accounts separately and
Each email address can only be connected to one Pinterest account at a time. If you temporarily deactivate a Pinterest account, it won’t free the email up for use on another account.
If you want to free up the email address on an account, you can:
At this time, there's no way to transfer or move multiple Pins between accounts. If you’d like to transfer Pins from one account to another you can save each Pin from your original account to your new account.