Undefined array key “user_id” in /var/www/wp-content/

Hello, for some reason I am getting this error at the top of wordpress.

Warning: Undefined array key “user_id” in /var/www/wp-content/plugins/user-avatar/user-avatar.php on line 637

Warning: Undefined array key “u” in /var/www/wp-content/plugins/user-avatar/user-avatar.php on line 638

How can I fix this please?

my website is https://www.winterhavenfoodtours.com