This error occurred if your server is running on 5 or less version of PHP, for the fixing that problem you need to contact with your hosting support team or change PHP version from cpanel.
Solution: Change your PHP version from Cpanel
Select PHP version from cpanel

Select PHP version from cpanel
php changing version to 7 from Cpanel
Select PHP Version 7.0 or 7.1 which is required and click on Set as current button.

php changing version to 7 from cpanel
If PHP version button not appear in your Cpanel so please contact with your hosting support team.