Have a look at the following steps and let us know how you get on!
Go to > Settings > Device > Date & time > Set date > Select the month, date and year then tap OK to set - to select, scroll to then tap the appropriate option
> Next, tap Set time > Select the hour, minute and am/pm then tap OK to set (to select, scroll up then tap the option you'd like)
> Tap Time zone > Select the appropriate option then tap OK. Tap Use 24-hour format to turn on or off (On when a blue line is present).
Hope this helps!