Warning Cannot modify header information

I’m having trouble logging into my WP admin. When I attempt to I get this warning

Warning: Cannot modify header information – headers already sent by (output started at /home/content/16/9880516/html/wp-content/themes/Clemin/admin/admin-interface.php:1720) in /home/content/16/9880516/html/wp-includes/pluggable.php on line 1121

I need help correcting this error.