how to change the icons in pages-menu.ts?

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Hi, I would like to ask how to use local icon in the page-menu.ts.
To be exactly:
I have a .png file in folder ./assets. In the page-menu.ts the icon is defined in the following part:
```
title: 'Forms',
icon: 'nb-compose',
children: [ ... ]
```
How could I use the png file as icon? Thanks for the help!