in England and Wales there is no obligation to be a rescuer (with a few exceptions). Until you intervene to try and rescue someone, you do not owe that person a duty.
As soon as you do intervene, however, you owe them a duty. Specifically, you owe them a duty not to make the situation worse
This does not mean that you'll be liable if you give someone first aid and in doing so, you make the situation worse. Duty is different to liability. Someone who intervenes may owe a duty not to make the situation worse, their actions would still be judged against those of a 'reasonable person' in the circumstances.
That test would take account of your skill and experience along with everything else going on