What to do before resetting Mac

1. Make sure that you make a copy of all necessary files. You can use Time Machine or Migration Assistant to transfer files to a new MacBook.
2. Sign out of iTunes. Open iTunes, from the menu bar at the top of your computer screen choose Account > Authorizations > Deauthorize This Computer. 
3. Turn off Find my Mac and sign out of iCloud. Choose Apple menu > System Preferences, click Apple ID, click iCloud in the sidebar, then deselect Find My Mac to remove your Mac. Then click Overview in the sidebar, then click Sign Out. Signing out of iCloud turns off all iCloud features on the device.
4. Sign out iMessages.  Launch the app. In the Messages menu bar, click on Preferences. Click the account you want to sign out in the left panel. Next to your Apple ID on the right click on Sign out.
5. Unpair Bluetooth  Go to the Apple menu > System Preferences and choose Bluetooth. Here you can unpair keyboards, headphones or other Bluetooth-enabled peripherals.
   
   Reset to factory settings
   1.  Make sure that Mac is currently connected to the internet via Wi-Fi and to a power supply via the power adapter, so there's no danger of running out of battery power. 
   2. Start the Mac and immediately hold down the Command + R keys until you see an Apple logo or spinning globe. Once you see the Apple logo appear, release the Command + R keys.
   3. You may see a screen asking you to choose a language. Select English.
   4. The next screen is Recovery Mode utility window.
   5. If the password is required when you select Disk Utility, do the following (opposite go to the step 6):
   — On the menu bar at the top of the screen, click Utilities
   — Click Terminal and type “resetpassword” in the prompt. Press the Enter button on your keyboard
   — Select the specific “Volume Hard Drive” in the top section of the window
   — Select the “User Account” that needs its password to be reset and enter the new password. Verify the password and click the Save button
   — Click OK when the prompt asks you to verify your actions
6. Select Disk Utility from the Utilities window in macOS Recovery. Then click Continue. You can see one or two disks here; it depends on OS. If you see two disks, go to step 6. If you see one disk, go to step 7.
7. You can see two disks — Macintosh HD and Macintosh HD-Data, you first need to delete the Macintosh HD-Data partition before erasing your main hard drive.

• Click on this Macintosh HD-Data drive to select it
• Then choose Edit > Delete APFS volume from the menu bar
• When you're asked to confirm, click the Delete button
• After deleting any Data volumes, select Macintosh HD in the sidebar and go to the next step.

8. Choose your startup disk (named Macintosh HD by default) from the sidebar and click the Erase button. Thereafter, complete items:
   • Name: Enter a name that you want the volume to have after you erase it, such as Macintosh HD
   • Format: Disk Utility shows the recommended Mac format by default.
   • Click Erase
9. Quit the Disk Utility
10. Select Reinstall macOS from the utility and follow the instructions that appear to reinstall macOS. When the setup wizard starts up shutdown Mac, so that the next owner can enter their details.
     

M1 Macbook reset instructions: 
Step 1: Enter the menu

1. Press and hold the Power button (Touch ID button) until you see "Loading startup options."
2. Select Options and click Continue.

Step 2: Erase the Disk

1. Once in Recovery Mode, choose Disk Utility from the list of options.
2. Select your startup disk (likely called Macintosh HD).
3. Click Erase.
4. Choose APFS as the format and GUID Partition Map for the scheme.
5. Click Erase to confirm. Once done, close Disk Utility.

Step 3: Reinstall macOS

1. Back in the main recovery screen, select Reinstall macOS.
2. Follow the prompts to reinstall the macOS operating system. The system will download the latest version of macOS compatible with your Mac.