How do I change the password encryption scheme?

Still working through difficulties upgrading to Dovecot 2.4. Right now I'm having trouble getting my mail client (Evolution) to connect; I keep getting "temporary authentication failures."

Before upgrading I was using the ARGON2I encryption scheme, so all my users' passwords are stored that way. How do I tell 2.4 to use ARGON2I by default? There used to be a "default_pass_scheme" parameter but that's apparently gone now. Any help is greatly appreciated!

Ken