If you are using MongoDB Atlas, you can select your Atlas cluster from the :guilabel:`Select a cluster` list, or you can enter the :manual:`connection string </reference/connection-string>`.
If you are using an on-premises deployment, you must use the MongoDB connection string.
.. tabs::
.. tab:: Select a cluster
:tabid: select-atlas-cluster
a. Select the cluster.
Clusters are displayed in a three-level hierarchy:
:guilabel:`Organization` > :guilabel:`Project` >
:guilabel:`Cluster`, organized alphabetically. Only the first 100 clusters you are authorized to access are shown.
#. If it isn't included in the connection string, enter the
:guilabel:`Database` to connect to.
#. If they aren't included in the connection string, enter the
:guilabel:`Username` and :guilabel:`Password` of your
:ref:`{+rel-mig+} MongoDB user <rm-mongodb-service-user>`.
Checking :guilabel:`Save password` saves the password securely
on your machine, so you don't have to enter the :guilabel:`Username`
and :guilabel:`Password` again when using the saved connection.
If you leave any of the form fields for :guilabel:`Database`,
:guilabel:`Username`, or :guilabel:`Password` blank, Relational
Migrator uses the values from the Atlas cluster metadata.
.. tab:: Enter MongoDB URI
:tabid: enter-mongodb-uri
a. In the :guilabel:`MongoDB connection string (URI)` field, input
your :manual:`MongoDB URI </reference/connection-string>`.
#. If it isn't included in the connection string, enter the
:guilabel:`Database` to connect to.
#. If they aren't included in the connection string, enter the
:guilabel:`Username` and :guilabel:`Password` of your
:ref:`{+rel-mig+} MongoDB user <rm-mongodb-service-user>`.
Checking :guilabel:`Save password` saves the password securely
on your machine. {+rel-mig+} automatically fills in the
:guilabel:`Password` field when updating connection information.
If you leave the form :guilabel:`Database`, :guilabel:`Username`,
or :guilabel:`Password` fields blank, {+rel-mig+} uses the
values from the URI.