Factory reset MacBook Pro is a little complicated than other devices, partly because there are more work about preparation, including backup, sign out iTunes, iCloud and other accounts.
1. Create a backup for your MacBook Pro
2. Sign out all accounts and services on your Mac
3. De-authorize iTunes.
4. Turn off iCloud.
5. Sign out FileVault.
You may need to sign out other apps, such as Adobe Photoshop, Netflix and more. And if your MacBook Pro has Touch Bar, you also need to remove any Apple Pay card information.

After backup and sign out various services, you can feel free to start factory resetting MacBook Pro
Step 1. Boot your MacBook Pro in Recovery Mode
Step 2. Erase your MacBook Pro's hard drive
Step 3. Reinstall Mac on your MacBook Pro
For detailed steps, please click: https://www.apeaksoft.com/tips/reset-macbook-pro.html