Migrating sync project to 9.0

After migrating from 8.1 to 9.0 IDM starts the DPR_Migrate_Shells jobs as expected to migrate the sync projects into the newest version.

The issue is that the credentials for the associated connections are wrong (sql users were changed), therefore the jobs are going frozen with this error message:

[810143] Database error 18470: Login failed for user 'oldsql_user'. Reason: The account is disabled.
[System.Data.SqlClient.SqlException] Login failed for user 'oldsql_user'. Reason: The account is disabled.

And changing them in the sync editor does not work due to the error message that the sync project is currently being worked on by a system process and saving is not possible, although the DPR_Migrate_Shells jobs were already closed with error:

Is there any way to change the connection credentials to fix this issue? Or any other way in general?

Thanks!