From the Nimbus Hosting dashboard, click on the cog icon next to your website to manage the hosting for that website.
Click on PHP.
On this page you can adjust your sites PHP version, memory limit, upload limit and also add custom PHP directives.
Some of the more common directives are short_open_tag, max_execution_time, max_input_time and max_input_vars. As shown below. Once you add a new entry, you must click 'Update Configuration' for it to be applied.
A full list of options that can be used here can be found on the link below.