Phrases to acknowledge being corrected in Mandarin
I would simply add 謝謝你 at the end to soften the tone.

我明白了，謝謝你。 I understand now, thank you.

原來如此，謝謝你。 Ah, so that's how it is, thank you.

"喔，知道了" can sound a little brisk and abrupt depending on your tone of voice. Adding 謝謝你 helps, but I would altogether use a different verb 明白, which is closer in meaning to "I understand now".