Under Menu > Manage > Schedules/Charts > Surfaces Scheduler.
You have a button at the top called Conflicts.
If you click on Conflicts, the system will list the matches that are in conflict.
Once you close our of the conflict Pop-up, you will see matches that are outlines in red.
Those are the matches that have a conflict.
You can click on a box (Match) and see the lines that are attached.
This will show where they are coming from and where they are going.
Other reasons for conflicts:
Surfaces is double booked. (Often, singles vs double surfaces)
Player scheduled at two places at the same time.
Once you fix the conflicts (change duration time, change start time, move match etc) You can click on Conflict again and see what is left. This will remove the red outline of matches that no longer have conflicts.
What this video for visual explanation of the conflict