Welcome to KH!
Thanks for the pattern link. At the beginning of the first set up row:
K1, m1, k19, p1, place marker and continue with charts (22sts in the section before the marker). Then at the end of the second set up row, after the last maker: k1, p21 (22sts).
The pattern doesn't want you to repeat the instructions for the set up rows again. It says to "work in pattern as established". When you continue the pattern as established the next row starts k21, p1, slip marker and continue next row of charts. That way both the beginning and the end of the row have 22sts. The m1 only happens once to get you to 22sts before the charts.