Check condition in checkout in Opencart 3.0?

Question

I am a beginner in OpenCart and Currently, I am using journal theme and I want make some condition that the customers don't allow to checkout if the shopping amount is less than 1000. Is this possible to make in OpenCart 3.0? If then, which controller, which view should I add code? Help me :-(

Updated:

<?xml version="1.0" encoding="utf-8"?>
  <modification>
    <name>Total Amount Checkout</name>
    <version>1.0.0</version>
    <author>Custom</author>
    <link>http://upencart.com</link>
    <code>total_amount_checkout</code>        
      <file error="skip" path="admin/controller/setting/setting.php">  // Do here, Is this the right path that I can make change? [I am using Journal theme]
        <operation error="skip">
           <search><![CDATA[ ******* ]]></search>  // Do here
           <add position="*******"><![CDATA[*******]]></add>  // Do here

        </operation>
      </file>
   <file error="skip" path="catalog/controller/checkout/confirm.php">
    <operation error="skip">
        <search><![CDATA[$redirect = '';]]></search> // Do here
        <add position="after"><[CDATA[]]></add> // Do here
    </operation>
</file>
  </modification>

In which path and what code should I add? Do something in above code based on my question.