Hi ​@Mari Nihongo, thank you for your post. You can enable pen by simply using a shortcut - “P”. If you would like to have it visible in the toolbar, you can click on the “+” button on the bottom of the toolbar and type “pen” in the search bar. I’m attaching an image of where to find it below. Please let us know if it answered your question :) 

Thanks so much for you kind answer :)
Honestly, I didn’t know about the shortcut, definitely will be using it from now on