Fix Joomla Template - Template not suitable for PHP 7.3

Hello, I have a Joomla Website. The Website is woking correctly, but in the backend a error message is shown: ===================================================== Error Message in Joomla Backend. We have detected that your server is using PHP 7.0.33 which is obsolete and no longer receives official security updates by its developers. The Joomla! Project recommends upgrading your site to PHP 7.4 or later which will receive security updates at least until 2022-11-28. Please ask your host to make PHP 7.4 or a later version the default version for your site. If your host is already PHP 7.4 ready please enable PHP 7.4 on your site's root and 'administrator' directories – typically you can do this yourself through a tool in your hosting control panel, but it's best to ask your host if you are unsure. ===================================================== When I change Php Version to later version, the template crashes. To-Do: Please fix the template so the PHP-version can be changed to to PHP 7.3.