Below are the steps to promote the changes from one ORS to another:
Step 1: Launch the jnlp file.
Step 2: Enter you credential, select the ORS.
Step 3: Under Workbench, select Repository Manager.
Step 4: Connect to Master Database.
Step 5: Under Validate tab, validate the ORS from/in which you want to promote the changes.
Step 6: Go to Promote Tab.

Step 7: In Source, select the option from which you want to promote the changes (Database repos or file repos(change.xml)).
Step 8: In Target, select the ORS in which you want to promote these changes.
Step 9: You can manually select and promote only those changes that are required in the target repos.
To Promote, select the object, right click, promote the changes.

Step 10: A window will pop up for merge conflict, you can select the best appropriate option for you and proceed.

Step 11: After you promote all the required change, click on apply changes.
Step 12: A window will pop up, asking Validate Data Integrity?, you can select yes or no as per your requirement.

Step 13. Once your migration is successful, validate the ORS.