Add the indicator Line Cross Alert to your chart. To assign values for the line, right-click on the chart and use the commands in the context menu:
The point where you right-clicked will be assigned for the value. First, choose the "LINE CROSS ALERT...: First" command to assign the first value. Then right-click on another point on the chart and choose "LINE CROSS ALERT...: Second" command to assign the second value.
You will see the line on your chart:
If you need to re-assign values, use the command "LINE CROSS ALERT...: Reset".