Changing customer review display name

Hi there!

I have found some code for child theme functions.php that will successfully display the name of customers whom leave reviews as “Firstname L” – however, I would like to change this so it actually displays as “F Lastname” (Initial of first name, entirety of last name)

This is the particular line in the code that I believe needs changing:

$author=$user->first_name.’ ‘.substr($user->last_name,0,1).’.’;

I started trying to figure it out by myself but got in a pickle!

Thank you for your help ??