Pup Sweater

I am confused with the following instructions, I am 19 rows into a “pup sweater,” and the instructions read:
p3,cast on 6 sts, p to bind off sts, cast on 6sts, p3.

I cannot figure out how to “cast on” so late into the project.

Thank you

Turn your work around and either do a knit or cable cast-on, then turn the work back and continue. Amy has video on both cast-ons.