In the document, all lines are in "Heading" style
Sample question .docx
Sample question.jpg
I am looking for a single click to split my selection into heading number, and put the "heading text" into next line.

After that, remain the "heading number" in "Heading" style
and change the 'heading text" to "Normal" Style.

Final outcome as below, Many thanks!!!
Sample (Final Outcome).docx