There are a few ways to approve messages needing moderation. 

- In your email, just reply to the notice and it will be automatically approved. No message is required, just an empty reply email. (You must be using your email address associated with the account (i.e. your account ID). 

-  Online, go to https://groups.io/g/GroupName/pending (or Admin > Pending.) 
From there, there are two options. 

1) Select the posts using the check boxes to the left of them and click the Approve (or another) button.

or

2) Click on the first one to open it, then use the buttons at the bottom to Approve, Edit, Reject, Delete, etc. 

Once you take care of the first, the next one will automatically open.