You'd think you were the one who did me the favour, and not the other way around.

你会认为是你帮助了我，而不是我帮助了你。

《柯林斯英汉双解大词典》

I hope I can do something for you one day to return the favour.

我希望有一天能为你做点什么来报答你。

youdao

Years later, I returned the favour.

多年后，我回报了这个恩惠。

youdao

and the same for favour, they spell f-a-v-o-r, we put u in it,

同样地，对于发烧这个单词，他们拼写成f-a-v-o-r，我们要加一个u在里面，

美式英语和英式英语 - SpeakingMax英语口语达人

People show consideration for others in the hope or expectation that the favour will be returned.

ECONOMIST: The benevolence of self-interest | The

In return they would either get a share of the spoils or simply have the favour returned.

ECONOMIST: Construction cartels

Now she must decide whether she will return the favour in her approach to the crisis in the eurozone.

BBC: The IMF and Madame Managing Director