1. Open toggle mentions feed and click on the diagonal arrows to open it in full screen.
2. Once that is open, click on the search bar in the top right. You can type which ever keyword you're looking for. This will make it so the only mentions popping up contain that keyword. Click on Edit post on the left side of your screen.
3. Select which posts you would like to delete by clicking on them. Once all your posts are selected. Click on the Red Trashcan icon and you're selected posts will be deleted from your monitor.