To turn off facial recognition on your computer, click on the down arrow at the top of any Facebook page and then select Settings. From there, click “Face Recognition” from the left column, and then click “Do you want Facebook to be able to recognize you in photos and videos?” Select Yes or No based on your personal preferences.

On mobile, click on the three dots below your profile pic labeled “More” then select “View Privacy Shortcuts” then “More Settings,” followed by “Facial Recognition.” Click on the “Do you want Facebook to be able to recognize you in photos and videos?” button and select “No” to disable the feature.
[…]
The setting isn’t available in all countries, and will only appear as an option in your profile if you’re at least 18 years old and have the feature available to you.

Source: How to Disable Facebook’s Facial Recognition Feature