you need the dbuser, dbpassword and dbname (from /var/www/nextcloud/config/config.php)
open your mysql commandinterface:
sudo mysql -u your_database_name -p
Enter your password: your_dbpassword
use your_dbname
show wrong records
select * from oc_jobs where reserved_at <>0;
update wrong records:
UPDATE oc_jobs SET reserved_at=0;
quit;