In this case, you need to knit your YO through its back loop (or back leg). This is called “twisted knit” and closes the gap or hole created in the previous row by making the yarn over.
Below I show you a series of photos that will guide you step by step.
1) Knit until you reach the YO you made in the previous row.
2) Insert the tip of your right-hand needle into the Back Loop (back leg) of the YO.
This may be somewhat uncomfortable the first few times, so be careful not to let the YO go of the left-hand needle while trying to catch the back loop 🙂
3) Knit normally the YO loop.
4) This is how it looks once knitted:
5) Some rows afterwards, you can hardly notice where the YO was, but you will have 1 more stitch in your needles 🙂