Change user password in AWS Babelfish

Question

I'm trying to change the password of a Babelfish login. In a psql session, I tried the following command:

alter role <username> set password = '<newpassword>'

But I get the error

ERROR:  Babelfish-created logins/users/roles cannot be altered outside of a Babelfish session

So I tried changing it with TSQL in a Babelfish session, logged in as <my_user>, with this command:

alter login <username> with password = '<newpassword>'

and I get this error:

Msg 33557097, Level 16, State 1, Line 12
must be member of "rds_superuser" to alter members of "rds_superuser"

And when I run this in psql

GRANT rds_superuser TO <my_user>;

I get this:

**NOTICE:  role "<my_user>" is already a member of role "rds_superuser"

I feel like I'm missing something obvious. Help!