Try this: Select the XML file in finder (so it’s highlighted in blue). Then click File (at the top of the screen). In the box that opens, click Get Info. (The shortcut to do all this is pressing Command and I at the same time). A box will open. Click on the blue arrows next to “Open with:”. Then click on TextEdit.app. Then click “Change All…”. Another box will open. Click “Continue”. That should do it.