How to get the Current datetime and update time part out of it to hardcoded value as 08:00:00 AM?

Question

Requirement is like get the current datetime and update on time to 08:00:00 AM and store it in C language.

For ex. If i am getting date as 02-Sep-21 12:48:03 AM then update it to 02-Sep-21 08:00:00 AM.

Can anyone help me. How to achieve this in C language?

P.S didnt get C lang tag so added C++.