If you want to reset or reinstall macOS on your MacBook Pro, then you have to first Erase the data from macOS Utilities and then you can again Install macOS. Steps are pretty simple and straightforward as explained below.
Steps to reset/format your MacBook Pro:
Step 1. Before you start the process, as a safety measure backup your data and a stable internet connection is needed.
Step 2. Choose Apple menu and click on Restart.
Step 3. While the computer restart, you have to hold down two keys they are “the Command (⌘) and R keys”.
Step 4. Hold them until the MacOS Utilities window appears.
Step 5. Then select “Disk Utility,” from the window and click “Continue”.
Step 6. Then select your startup disk from the list on the left-hand side. And then click on “Erase” tab.
Step 7. A new window will appear, select Mac OS Extended (Journaled) in field and type in a name for your disk and then tap “Erase”.
Step 8. Once the Erased task is completed. Opt out by choosing Disk Utility and clicking Quit Disk Utility.
Step 9. As mentioned above, an internet connection is required. Connect to your network from the Wi-Fi menu in the right-hand corner of the menu bar.
Step 10. Then Select Mac OS X, click “Continue”.
Step 11. Follow the simple instruction to reset your MacBook Pro. Don’t put the laptop on sleep during the installation.
Note: You need to install macOS Sierra 10.12.4 or later to follow these steps.