Data quality is an assessment of data's fitness to serve its purpose. To use this functionality, you can enable patterned responses module under the Data quality module. This module will perform the quality check for matrix questions against the responses selected in straight line or zig-zag pattern for matrix questions.
If you think the response should not have been flagged, then you can unflag the response by clicking on the response ID. Navigate to the data quality tab. You can see the question, answer and the reason for flagging the response. Click on the Unflag Response button. Once the unflagging is done the flag icon will disappear in the response viewer.
To flag the response, click on response ID. Navigate to data quality tab. Click on Flag Response button. Once the response is flagged, flag icon will appear with response ID which has been flagged.