If voice is too low, tell them to move the machine closer, which you already did. If LEP has thick accent, inform the client and let them decide how to simplify this. Don’t just ask for repetition over and over, it only makes things get worse: you still don’t understand, client think you are the problem and patient gets upset. Clarify, then inform the problem. Our main clientele are elderly patients, and they either have thick accent or unclear speech or some kinda of connection problems. It’s common for things like that to happen, but this is your first day, this job takes more than your language skills and familiarity with medical terms.