I’m not quite sure what the pattern wants me to do…
Round 30: At the beginning of this round, use contras:ng scrap yarn to knit 7 stitches
Transfer these seven stitches back to left needle and continue knitting, knitting across the contrasting stitches as part of the
round.
Thumb: At contras:ng s:tches, use double‐pointed needles to pick up 7 s:tches on the boFom and 6 on the top.
Carefully remove contras:ng yarn.
Pick up two s:tches on each side of thumbhole, 17 s:tches total.
Help?
It’s one of those things that will make sense eventually. Just knit the 7 stitches with a contrasting yarn, not your working yarn. When they have been knit and are on your right needle move them back to the left needle and knit them again, but this time with the working yarn.
When you’re done with the mitten and are ready to do the thumb you’ll pull that contrasting yarn out and it’ll leave a hole with live stitches. Put those live stitches on your needles and now you’ll be knitting just the thumb.
Trust me, it works. 
You’re using the contrasting, scrap yarn to hold the sts for the thumb. When you go back to the directions for the thumb, you can carefully pull out the scrap yarn and as you do that, st by st, pick up sts with two of your dpns, one needle for the top sts and one for the bottom sts. You’ll have 6sts on one needle and 7sts on the other. Then you can continue the thumb directions, distribute the 13sts over 3 needles and pick up two sts in each gap between the original top and bottom sts.