Below are the steps to validate an ORS:

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: Select the repository to validate and click on validate button on your right.

After clicking the validate button, MDM Hub performs the metadata validation and gives you the results for validation as:
Error: You can see a red cross, on the ORS after validation, the ERRORS tab indicate about the error that persist in the ORS.
Warning: You can see a yellow color symbol, on the ORS after validation, the WARNING tab indicate about the warnings that persist in the ORS.
Apart from these you will see a question mark on the ORS that indicates that your ORS is not validated after the changes you made.