If row 1 is the right side then row 4 would be a wrong side. I think you just knit 3 rows and then purl the 4th row, putting a Reverse stockinette row on the wrong side on that row and a stockinette row on the right side. This all ends up with a small border of garter stitch and possibly a beginning of stockinette thrown onto the right side or whatever they ask you to do next.
If, as you say, when you are ready to work the 4th row you have the right side facing you, you could purl the wrong side of it by putting the stitches on another needle (if you are on straight needles), or simply moving the stitches to the other end of the needle if you are using a circular needle. Now the wrong side is facing you and you could purl it. You would need to join a new yarn to do this, but it is simple to do.