You can’t until you reach Trust Level 3 (“Regular”)… so what you did is OK. Here’s a clickable version of it:
Then you should move the entire topic to the PTR Bug Report category – this category here is for the live game.
To move your topic, scroll up to the title and click on the pencil tool to the right of it. That will allow you to change the category from “Bug Report” to “PTR Bug Report”. Then click on the button to approve the change and move the topic.