To humbly visit or present oneself to someone of higher status; often used in the form 'to come' or 'to arrive' in a polite/old-fashioned way.
ただいま参上しました。お待たせして申し訳ありません。
I have arrived; sorry to have kept you waiting.
殿、拙者、参上！と言うような戦国時代を舞台にした台詞を聞いた。
I heard a line from a Sengoku-era drama like 'My lord, I have arrived!'.
重要な会合には時間どおり参上することが求められる。
You are expected to be present at important meetings on time.