Copy the extension to phpBB/ext/davidiq/multitopicicons
Go to "ACP" > "Customise" > "Extensions" and enable the "Multi-Topic Icons" extension.
Go to "ACP" > "Forums" > Add or modify existing forum > Max number of topic icons > Submit
Copy the extension to phpBB/ext/davidiq/multitopicicons
Go to "ACP" > "Customise" > "Extensions" and enable the "Multi-Topic Icons" extension.
Go to "ACP" > "Forums" > Add or modify existing forum > Max number of topic icons > Submit