If the patient is able to say "Please help me, I can't breath," they can breath
Absolutely you would give them appropriate care to relieve their distress, be it position changes, medication, comfort measures, etc. Like others have mentioned, DNR measures is what happens upon respiratory or cardiac arrest.
I think one thing a lot of nurses think (especially where I work in the ICU) is, "OK, the patient's a DNR and/or DNI, great!" and they don't address how the patient wishes to be treated while they're still alive. Some prefer to have full aggressive treatment, others want comfort/palliative care measures, some want chest compressions, some don't, some want to be shocked, some don't, some want pressors, some don't... Don't forget to address how the patient wants to be treated before they die! That is, after all, what a lot of nursing care is about! If you aren't sure, ask the patient or whoever is making decisions for the patient.
If the patient is alert and competent, they can absolutely revoke their own DNR order.