design outline edit

Try this: 

- In Edit -> Change ... , right click on the line you want to edit. Then choose "Cut". 

- Pick the two cutting points (in your case, the ones you are marking inside the red circles)

- Then go to Edit -> Delete and make sure that in your Find panel, you have selected "Other segs." only. 

- Double click on the segment you want to delete

test_brd_02.zip

I can't select the segment.I don't know why. It says no element found. 

You can't select the segment because there isn't one. You have an "Outer" Shape for Design Outline and Shapes for Cutout(s). You need to convert the Shapes to Lines, Shape>Decompose Shape, then you can edit the Lines as described. Once you have the required Lines, you can use Shape>Compose Shape to get the final Design Outline Shape. This isn't really necessary since the Cutout can be processed by the fabricator to remove the material of the Cutout(s). See the notes on the Cadence Support site on handling Cutouts and fabrication data.

Yes, just like oldmouldy said, you might need to first decompose the shape and then apply the cut. 

Other things to have in mind ... check your Find panel filter, the mode you're in (you should be working in General Edit or Shape Edit Mode to avoid deactivating certain items in the Find Panel), use Show Element to see what you're trying to select ... then you can take action accordingly.

Nevertheless, as oldmouldy says, check the Cadence Support website on handling cutouts and fab data.