Error Message - Only variables should be assigned by reference

Hi,

I have upgraded my site to Joomla 3.9.6 and get the following:

Strict Standards: Only variables should be assigned by reference in /var/www/vhosts/http://xxx.yyy.zzz/httpdocs/plugins/jevents/jevcalendar/jevcalendar.php on line 12

Strict Standards: Only variables should be assigned by reference in /var/www/vhosts/http://xxx.yyy.zzz/httpdocs/plugins/jevents/jevcalendar/jevcalendar.php on line 12

Strict Standards: Only variables should be assigned by reference in /var/www/vhosts/http://xxx.yyy.zzz/httpdocs/plugins/jevents/jevcalendar/jevcalendar.php on line 182

Strict Standards: Declaration of jevCalendarFilter::_createFilter() should be compatible with jevFilter::_createFilter($prefix = '') in /var/www/vhosts/http://xxx.yyy.zzz/httpdocs/plugins/jevents/jevcalendar/filters/Calendar.php on line 80

Strict Standards: Only variables should be assigned by reference in /var/www/vhosts/http://xxx.yyy.zzz/httpdocs/plugins/jevents/jevcalendar/filters/Calendar.php on line 31

Strict Standards: Declaration of jevMulticalendarFilter::_createFilter() should be compatible with jevFilter::_createFilter($prefix = '') in /var/www/vhosts/http://xxx.yyy.zzz/httpdocs/plugins/jevents/jevcalendar/filters/Multicalendar.php on line 89

Strict Standards: Only variables should be assigned by reference in /var/www/vhosts/http://xxx.yyy.zzz/httpdocs/plugins/jevents/jevcalendar/filters/Multicalendar.php on line 31

Can you please let me know what I need to do to fix this issue please?

Regards,

Bob