I could not have fixed it if you had not told me, so thank you.
ご質問ありがとうございます。
"I could not have fixed it"＝「私はそれを直すこおとはできなかった、」
"if you had not told me,"＝「もしあなたが私にそれを言わなかったら、」
"so thank you."＝「だから、ありがとう。」
☆他にも同じパターンの例文です：
"He could not have bought a house, if I had not worked hard for many years."＝「私が何年も頑張って働いていなければ、彼は家を買えなかった。」
ご参考に。
If you hadn't said anything I wouldn't have been able to fix it, thank you.
"言ってもらえなかったら直せなかったからありがとう"
- If you hadn't said anything I wouldn't have been able to fix it, thank you.
- Thanks for saying something. I wouldn't have known to fix it otherwise.
- If you didn't point it out to me, I wouldn't realize it was something I had to work on, thanks.
アメリカ合衆国 
