Error after installing JsTrackerCustom

Hi, I have the latest version 3.13.5, the installed (core) plugin CustomPiwikJs is not working anymore in this version as per this forum, so I installed a plugin from the marketplace called JsTrackerCustom which does the same job.
After installing I got the following error:
“To be able to add custom JavaScript, the file /././html/plugins/JsTrackerCustom/tracker.js needs to be writable”
I could not find this file in the specified plugin folder.
So I ignore it, I tried to save a js code but I get the following error:
“WARNING: /./././html/plugins/JsTrackerCustom/Controller.php(50): Warning - file_get_contents(/./././html/plugins/JsTrackerCustom/tracker.js): failed to open stream: No such file or directory - Matomo 3.13.5 - Please report this message in the Matomo forums: (please do a search first as it might have been reported already) (Module: JsTrackerCustom, Action: index, In CLI mode: false)”
Can you please help. Thanks

Let me write the question in other way: Is there is a way to edit piwik.js file in order to add additional js code?