While your in the editor on the left hand side you should see all the sub-folders for the entire mission. These can be locked inorder to prevent mishaps in movement when you're working with larger structures. You need to find the folder with the Trench's in them and click on it. When you have the folder selected along the bottom of that rectangle menu you need to click the lock along the bottom that will unlock the sub-folder and allow you to do as you wish.

For those that need help

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