In order to check the box to enable the Estimated Price Range on your chart, you will first need to enable the "Margin area" of the chart. This can be found by clicking Edit followed by Global Chart Configuration and selecting "Margin area" in the Display section. Be sure to click Apply and OK once finished. You can then activate the Estimated Price Range feature by selecting the Edit menu option followed by Chart Parameters, and clicking the Estimated Price Range box under "Additional Data and Features" followed by Apply and OK.
For additional information on the Estimated Price Range function and setup, please see the TWS Users' Guide.