The time is automatically set and displayed on the LG device over the network, so if you want to change the time manually, you must first disable the automatic time.

Android 9 | LG UX 9.0
Change time -  Open the  Settings
Change time -  Tap on  General
Change time -  Tap on  Date & time
Change time -  Disable  Set automatically
Change time -  Tap on  Set time
Change time -  Set  Time  and confirm with  OK
  1. Open the Settings
  2. Tap on General
  3. Tap on Date & time
  4. Disable Set automatically
  5. Tap on Set time
  6. Set Time and confirm with OK

LG Instructions