Double mono output on a PC

You typically have a stereo mini-TRS out on a PC. You can buy a simple “splitter cable” that will split that stereo out into 2 mono-TRS outs. Then you need to adjust the sound routing in your DJ software accordingly and you can go from there.
Please check also out Phil’s free videos on youtube, where explains that in detail, just search for “digitaldjtips dj free dj course”.