This feature is only available in the desktop editor.
Create target article
Open article with steps you want to move
You should now have two articles open.
Option 1: Copy and Paste
With both articles open you can copy select the content you want to copy and use Edit > Copy to copy the content to the clipboard. Now switch to the new article and use Edit > Paste to paste the content.
Option 2: Drag steps from one article to another
If you want to copy the steps, hold down the option (Mac) or alt (Windows) key while you drag the steps.
The steps are moved to the new article. In the screenshot below the content was copied from one document to the other.