infected file

I received an email yesterday from my internet provider “that an infected file was discovered due to the presence of an outdated application or script in your account.”

I went into my files and saw this:
Scan started at – Sat Nov 17 07:55:10 EST 2018
/public_html/dorothytanner.com/wp-content/themes/graphene/functions.php: SiteLock-PHP-INJECTOR-1-eyv.UNOFFICIAL FOUND

———– SCAN SUMMARY ———–
Infected files: 1
Time: 1591.312 sec (26 m 31 s)
Scan ended at – Sat Nov 17 08:21:41 EST 2018

I am wondering how to identify and remove the file.
Thank you for any help!
Barry
[email protected]