If you've moved to a different Region of Residence (RoR), you can transfer your Shard so that you can matchmake with players in your new region.
To transfer your Shard, log in to Legends of Runeterra (without VPN), then Submit a Ticket (choose "Account Management") stating which Shard you want to switch to.
One caveat, though! When your Shard is transferred, you'll lose all progress in Labs. Other than that, don't worry—you'll keep all your decks, cards, and unlocks.
Note: Once you transfer your Shard, you won't be eligible for another transfer for 90 days.