When you work to three stitches before the marker you end up with your decrease, and then a regular stitch at the end, before the marker. Then you have a regular stitch and a decrease after the marker.
So work to three stitches before your marker, do the decreses before and after it.
Then work three rows even, as you had been all along.
This set is made of four rows, one dec row and three straight rows.
Work this set of rows 4 times.
This way you get a gradual decrease.