Are you referring to "Select Value" modal to select a test plan? The entries here are based on the Request URL and Display values for the data source in RPE template (right click and choose Edit Configuration Metadata... in RPE Studio).
For example:
Identifier: feed/entry/id
Display: feed/entry/title
Request URL: ${public}/service/com.ibm.rqm.integration.service.IIntegrationService/resources/${projectAreaUUID}/testplan?fields=feed/entry/content/testplan[title='${userInput}']/*&wildcard=*
will result in the following window:
You can enter search text with wild card so as to filter the test plans.
As you cannot use variables while configuring metadata, you cannot filter out the entries automatically.
