This is so much easier to do in person. I’m not sure about this but give it a try.
Pull the long multi-color strand through the multi-color stitch at the tip of the right needle so it is a knit stitch. Use a crochet hook or another needle to reach under the multi-color loop (blue dot), grap the blue loop (red dot) and pull it through. Place the blue loop on the right needle and put the long multi-color loop over it (as a yarn over).
Then turn to work the round with the blue strand.
I know you said you didn’t want to cast on again, but as you’re only 1 row in, that’s probably what I’d do.
You might also consider making a swatch to practice picking up dropped stitches. You could use any yarn at all for this, maybe in high-contrast colors.