How do you upgrade from mariadb 10.2 to mariadb-galera 10.3 in kubernetes?

Hello, I am using mariadb 10.2 as a container in kubernetes, and what i want to do is upgrade to mariadb-galera using the official mariadb-galera helm chart, while keeping all my data. I tried setting existingClaim to point at the volume used by the 10.2 installation, but this failed because it said it was not safe to bootstrap because the grastate.dat file was not found. So then i tried setting bootstrap.forceSafeToBootstrap to true as well, but the same error persisted. Is it possible to upgrade just by pointing at the same volume, or do i have to do something more involved, like exporting the data using an sql client, creating a new volume, and then importing the data back with sql?