How do I access the list of available add-ons?

Click button at the bottom of the list.
Once the store loads, it will be divided into several sections:
1. Bundles: this section shows you items that have been grouped into a single purchase.
2. Single Items: this section shows you individual items that are available for purchase.
3. Purchase History: this section shows your purchase history.
To restore your previous purchases, the restore button at the bottom of the list then follow the instruction provided by Apple