Sometimes, even when you know you should stop and periodically check things, you don't. Which is why I'm going to drop stitches into the prior row of squares in my entrelac to recapture a split stitch. (I am writing this portion before editing the fabric. Optimism is high.)
Here we see nearly identical pictures of the work, the first is unedited so that you can see the active square which is started from the selvedge of the square where the spare DPN is inserted into the split yarn that is not joined to the stitch above. The second has a line drawn showing the path I will need to take from the active stitches down into the knitting.
Note: I like joining my entrelac squares a little bit differently than I typically see instructed. When picking up the stitches for the new square typically you would pick up the stitch so that the selvedge is on the wrong side. I like to pick up the stitches so that the selvedge shows on the front of the work and the color of the next row gives a little decorative detail.
Stage one of the drop back. Since that first stitch has a lot going on, being the edge stitch and where the yarn transitions to the next square, it gets a red stitch holder to make sure that nothing's coming loose and is easily identified. I'm not completely detaching the two squares, just disconnecting the selvedge stitches until I get back to the column on the adjacent square I'm going to have to drop back on, which is at the gap at the right side of the stitch holder.
We have arrived! Now to rework the split stitch and then put it all back together.
Fixed! The crochet hook is pointing at the reworked stitch, which is a little bulky. When I started reworking that column of stitches I realized that I had a little bit more yarn in that spot than I wanted to leave so pulled up the yarn and formed an extra stitch which was then worked as a k2tog to tuck away the excess. It's a little bulky but there won't be a hole and unless you're feeling the fabric you probably won't notice it.
I think in theory you could use the same sort of technique to drop back to an even earlier row of squares, but hopefully I won't need to test that out anytime soon.