To learn about how an acoustic model is adapted you probably want to check out the CMU Sphinx project, since that isn’t something I can support from here beyond pointing you to the docs at the CMU project since it isn’t part of OpenEars: http://cmusphinx.sourceforge.net/wiki/tutorialadapt
The corpus of speech you would want to use in order to adapt to a UK accent for your particular application would have a number of different speakers with the desired UK accents saying the words for which you want more accuracy (I would have them say all of the words in your language model). Basically you will want to make recordings of your speakers saying the words and then you will use the acoustic model adaptation method linked above to integrate their speech into the acoustic model. The result ought to be that your adapted acoustic model will get better at recognizing/distinguishing between those words in the accents you include. The acoustic model you end up with can be used with OpenEars just like the default acoustic model.