Prepare the slow cooker liner with nonstick cooking spray. Inside the slow cooker liner, place the potatoes. Pour oil over the potatoes. Then, add the garlic, oil, salt, and water. Toss the potatoes to coat evenly. Cover the slow cooker and cook on high for 3 to 4 hours. When the potatoes are cooked through, beat the potatoes inside the slow cooker liner using a handheld electric mixer. Stir the cream cheese into the potatoes. Then, add the milk a little at a time until you like the consistency. Stir in the chives, sprinkling some over the top, and serve.