Collar help

The only thing I have left to knit on my sweater is the collar. I was supposed to put 42 stitches form the front piece and 42 stitches from the back piece on holders, and these are what I put on circular needles to knit the collar. I watched the video on circular knitting (I’ve never done it before), and I think I understand it, but when I transfer the stitches over to the circular needle neither end is going to be connected to the ball of yarn, so I don’t know how I can knit it. Please help me (in as simple terms as possible). Thanks!

Disconnect the yarn from where it is and reattach it to the beginning of the round. Simple.