How can I make my own vinegar?
Although you can hope that the right bacteria will get from the air into a bottle of wine you left open, you will get quicker and more reliable results using unpasteurized cider vinegar. Unpasteurized means there should still be plenty of the needed acetobacter.

Pour your vinegar half and half with red wine in a container that you leave open (but with cheesecloth to prevent bugs and all to get inside) and let it sit in a dark spot 2-4 weeks.

Different sources recommend using solution with a 5-7% alcohol content, so any wine (typically ≤15%) diluted by half with vinegar should be fine.