Becky,
otk_user is not a ca-provided user so I assume its the user created for OTK. So you would need to update policy manager -> Tasks -> Manage Data Sources -> Manage JDBC
On Gateway its a ca-provided user so it doesnt have a JDBC data-source.
The following link tells you to reset the connection string for the Gateway (which need to be done on all processing gateways)
Managing the MySQL privileged ('root') and unprivileged ('gateway') user accounts
And of course any scripts that you have provided the gateway user / password is also required.
Hope that helps.