You can change custom fields as metadata for a particular site by setting up metadata navigation for a list or library.
To do this, you must first enable metadata navigation and filtering on your site if it is not already enabled. You can do this by clicking on “Settings”, then “Site Settings”, and under “Site Actions”, click on “Manage site features”. In the “Features” list, find “Metadata Navigation and Filtering”, and then click “Activate”.
Once metadata navigation and filtering is enabled, you can navigate to the list or library for which you want to configure metadata navigation and click the title.
Click “Settings”, then click “List Settings” or “Library Settings”. Under “Permissions and Management”, click “Enterprise Metadata and Keywords Settings”. In the “Enterprise Metadata and Keywords Settings” section, click the “Enterprise Keywords” checkbox to add an Enterprise Keywords column to the list and enable Keyword synchronization. Click “OK”.
I hope it helps!
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