In a multi-tenant system, you are able to apply search filters from the default tenant to other tenants or you can log in the relevant environment and apply filter only on the logged in tenant.
Search from the default environment
If you are logged in to the '0000' default environment you will find an additional field under the Search page's Advanced Search Option segment of Criteria panel, this is the 'Environment' drop down field.
Here you can select the environment you would like to apply your search filter to.
You can find out further information regarding using the Search panel in Searching conversations article.
Search in the desired environment
If you are logged in to the relevant environment, you also use the standard guide of Searching conversations.