First, you will need to add your preferred star. (I will use the Sun)




Next, add your planet at preferred height. (Below red or mid-red height not recommended)

Press the Binary option on the Add Tool. Now select a star of mostly to equal mass. Check Balance Motion for best stability, and place the star at the preferred distance.




Now the planet should adapt to it's new orbit with a binary system!

So even though it is now orbiting both stars, the orbit has changed.





You can try to tweak this yourself and make it more circularized, and make your system the way you like it.