This is for a little split on a side seam, like on a pair of capri pants.
For this sample, I used a 2" hem (after turning under 1/4" it's
stitched at about 1.75"), with a 1" split.
Sew up your side seam, stopping at split
Turn up hem, RST, and sew, stopping at end of seam you just sewed
This is what the other side looks like.
Sew remaining hem allowance RST.
Flip split out, and press seams open (both pant and hem), press, stitch hem.
This is the finished split, right side