Hi [Name], sorry, I’m still not quite sure what fix we need to make. Could we have a quick meeting so you can explain it to me?
A slightly more polished version:
Hi [Name], sorry, I’m still not completely clear on what fix we need to make. Could we have a quick meeting to go over it?
Notes:
“I beg your pardon” is very formal and can sound old-fashioned here. Use “sorry” instead.
“Explain me the thing” is incorrect. Say “explain it to me” or “explain the issue to me.”
“Short meeting” is okay, but “quick meeting” sounds more natural in workplace chat.