system nodiccall php 7

This work must be initiated within the next few hours, and it must be completed within the next 6 hours, otherwise the project becomes closed as not completed. We have upgraded our sever from php 5 to php 7, and now we have an error on our page, which we wish to get corrected. Fatal error: Uncaught Error: Call to undefined function simplexml_load_file() in /var/www/XXX/web/model/[login to view URL] Stack trace: #0 /var/www/XXX/web/model/[login to view URL](47): GeneralSettings->__construct() #1 /var/www/XXX/web/model/[login to view URL](25): LiveSettings->__construct() #2 /var/www/XXX/web/model/[login to view URL](29): SetupFactory::getSettings() #3 /var/www/XXX/web/controller/[login to view URL](41): Logger->__construct() #4 /var/www/XXX/web/[login to view URL](33): Controller->__construct() #5 {main} thrown in /var/www/XXX/web/model/[login to view URL] on line 53 The work must be performed via teamviewer, where you log into the server via commando promt on our PC via teamviewer