You can use adb to do this without root (But you need a PC). First download Android platform tools from https://developer.android.com/studio/releases/platform-tools now unzip them in a folder in your PC.
Go to that folder and open Command Prompt. Now in your phone, find the build number and tap it 7-8 times to enable Developer Options. Now open Developer Options and enable USB debugging. Then plug your phone with your PC. Confirm the box.
Now first type
adb devices. Then enter the command
adb shell to start adb shell. Now type the command
pm list packages | grep "clock" or if you have problem with grep then use
pm list packages | find "clock". Find the package name of default clock. Now use
pm uninstall -k --user 0 package-name. If you see Success message, then clock app will be removed.