My recipe said to cook the chicken on high for 1 hour then low for 5-6 hours. I forgot to change to low and it was on high for almost 2 hours. How do I adjust the time on the low setting now?
Make sure nothing burned onto the sides (scrape it out if necessary), and add extra water if too much has boiled off.
After that, I'd probably check it after 3 hours on low, pretending that the hour on high cooked it twice as much as it would have on low, and see if you think it's done. No harm letting it go the full remaining 4-5 hours if it seems like it needs it, or like it won't hurt.
The recipe probably isn't very sensitive anyway; there's a good chance even if you had followed it exactly you'd think it was fine over a pretty broad time range.
...all that said, a chicken cooked on high for one hour and low for one hour sounds like it'd probably be done to me. I'm not sure why the cooking time is so long, and you could honestly just check it right now.
First, I'd check the insides to make sure that you aren't burning around the edges. Some long cook times on high can evaporate the liquid out (even when covered) and create a very stubborn burn ring around the inside.
That aside, crockpot cooking is not a very sensitive or precise method of cooking. I'd say to reduce the temp to low and ride out the rest of the time. Everything in there is simmering either fast or slow: But it is intended to simmer for the total time, regardless.
So my answer: 2 hours on high, followed by 4-5 hours should be a fine equivalent. And you'll still be right on time! :-)