From this page of the Gwent Rogue Mage game guide, you will learn how to change your deck before starting your next journey.
Each player starts their adventure with Gwent Rogue Mage with one deck, which can be strengthened during expeditions by adding new cards. It should be noted here that the deck can be changed only after the end of the session, before you start the next expedition.
There are 4 basic decks in Gwent Rogue Mage, which are unlocked at certain experience levels:
- Bastion: available from the beginning of the game.
- Savage Fury: available after gaining level 15.
- Hive Mind: unlocks after reaching level 25.
- Chaos: available after reaching level 45.
Before an expedition begins, click on the map on the lab table - you will be able to decide which of the available decks you want to use next.