You have different options to add a stamp to your collections.
From already available collections and stamps
Click on My Profile link as below.
You can see all available collections and stamps that you have published or created.
- Click on any stamp and you can add this stamp to the required collection
- Click on any collection and you can add stamp to this collection
When you add a new stamp
After you add a new stamp, you see an option to add it to a collection. Click on plus icon available at the bottom right side of the screen. The right sidebar expands as below.
In My Collections, you can see all the collections you have created in your account. Click on Add button available in the collection and the stamp is added to that collection.