英语翻译：昨天是我帮助了你

It's me who helped you yesterday

It was me who had helped you yesterday.
主句用一般过去时，从句用过去完成时，我昨天帮了你是过去已经完成的动作

I helped you yesterday.

It was me who helped you yesterday。

The one who helped you yesterday was me!

It was me who helped you yesterday.
强调句，who也可以换成that