Website broken after update – PLEASE HELP

Hello,

I have updated some plugins and now receive the following error on my website https://www.kidzone-kinderbetreuung.de:

Notice: Undefined index: hide_sharethis_terms in /customers/b/f/c/kidzone-kinderbetreuung.de/httpd.www/wp-content/plugins/simple-share-buttons-adder/inc/ssba_admin_bits.php on line 7

When I try to login I recieve the following message and can not login:

Notice: Undefined index: hide_sharethis_terms in /customers/b/f/c/kidzone-kinderbetreuung.de/httpd.www/wp-content/plugins/simple-share-buttons-adder/inc/ssba_admin_bits.php on line 7 Warning: Cannot modify header information – headers already sent by (output started at /customers/b/f/c/kidzone-kinderbetreuung.de/httpd.www/wp-content/plugins/simple-share-buttons-adder/inc/ssba_admin_bits.php:7) in /customers/b/f/c/kidzone-kinderbetreuung.de/httpd.www/wp-includes/pluggable.php on line 1174

I would appreciate I you would help me how to solve that issue.

Thank you in advance and kind regards
Marc