Co-washing is really simiple.... at least for me.
All I do when I co-wash is use a cheap conditioner either vo5 or Suave will do. Run the water over my hair for a minute or two letting it get completely saturated and then ring out the excess water. Then I apply a very liberal amount of whatever cheap conditioner to my hair and take my shower. I sometimes detangle my hair at this point if needed then rinse it out. I bloat my hair with a towel and then proceed to let it air dry 50% before applying my leave-in, moisturizer, and sealing oil.
I co-wash mid-week and shampoo/DC over the weekend.
HTH
Here's a thread asking about the same thing: How to co-wash