To 'reverse' shaping you put the decreases on the other edge of the piece. On the first one you might have done decs at the beginning of a knit row, so for the other piece, you do them at the end of the knit row. If the pattern has you BO stitches, you can't do them at the end of the row, you would have to do that at the beg of the next row which would be the purl row.
The pattern pretty much explains how to get started though - beginning second piece with a purl row & working all subsequent knit rows as purl & all subsequent purl rows as knit - so you would just read the pattern the opposite of what's written for the first piece. You would start by purling a row instead of knitting it and just do purl rows instead of knits, or knit rows instead of purls.