Note: Each of the following steps should be performed in quick succession.
How to force restart iPhone XS, iPhone XR or iPhone X
Step 1: Press and release the Volume Up button.
Step 2: Press and release the Volume Down button.
Step 3: Press and hold the Side button and continue to hold until the device reboots.
How to enter DFU mode on iPhone XS, iPhone XR or iPhone X
Step 1: Connect your iPhone to your Mac (or PC with iTunes installed) using a Lightning to USB cable.
Step 2: Press and release the Volume Up button.
Step 3: Press and release the Volume Down button.
Step 4: Press and hold the Side button for 10 seconds until the iPhone’s screen turns black
Step 5: While continuing to hold the Side button, press and hold the Volume Down button for 5 seconds, and then release the Side button while continuing to hold the Volume Down button for an additional 10 seconds. The screen should remain black if performed correctly.
Step 6: Open iTunes, and you should see a message stating that “iTunes has detected an iPhone in recovery mode. You must restore this iPhone before it can be used with iTunes.”
How to Enter Recovery Mode?
Connect your iOS device with 3uTools, then find "Enter Recovery Mode" in 3uTools. Then you could be able to enter/ exit Recovery Mode by one click.
How to exit DFU mode on iPhone XS, iPhone XR or iPhone X?
Exiting DFU mode is a bit more involved than exiting normal Recovery mode.
Step 1: Press and release the Volume Up button.
Step 2: Press and release the Volume Down button.
Step 3: Press and hold the Side button until the Apple logo appears.
Note: You can also use this same method to exit out of Recovery mode
You may want to check out:
How to Put Your iPhone8/iPhone 8 Plus/ iPhone X In DFU Mode?
How to Enter DFU Mode and Recovery Mode on your iPhone 7 & 7 Plus
How to Put iDevice in DFU Mode, Recovery Mode and Normal Mode?