You can check the number of unopened Charm Packs on the Charms Tile in Lobby. Once you enter Charm Arena, all your stored Charm Packs will open automatically.
Each Magical Pack will offer an option to re-open the pack. Use the "Reopen” button to reshuffle the Charms inside your pack. Choose it wisely because there is always a chance to get the same charms or to get new charms - good luck!