Hello
That’s a bit of a tricky one to come across isn’t it?
One way to do this is to turn your work without having done the YO.
Then place the yarn over the top of the left needle, producing the YO, and anchor it with finger or thumb to keep it in place.
Then you need to purl into it. Without letting the yo slip off the left needle bring the working yarn to the front, between the needles, as you normally would in preparation for working purl stitch. Purl into the YO.
So long as you hold that YO strand on the left needle until after the purl is performed (insert needle, wrap, draw new stitch through) you will make a purl stutch with it. When you let the YO strand drop off the left needle you should have a new stutch kn your right needle and can then continue with the next stitch.
It might take a few tries to get it. The good news is that with it being at the beginning of the row if your stitch doesn’t work out right you can just drop it off the right needle, it will undo, and you can try again. The rest of your knitting won’t be effected.
If you find it too tricky you might be able to replace it with a kfb (knit front and back into the first stitch) to make the increase. If you are not sure about this let us know, someone will be able to help.
What pattern are you making?