Go to Colleges.
List of colleges will appear.
Click on the name of a college which is already added or you want to add
The page of that particular college will appear as shown below
Go to Additional Details highlighted above.
Click on Edit and select the relevant tag.
Once a field is selected, it will appear as a tag for the college on the previous page where the list of all the colleges is available as shown below
Go to filters on the left hand side.
Go to custom fields as shown below
Select the relevant tag and click on apply filter