# Extracting amplitude of signal from FFT plot

I am busy with to extract peak amplitude of a noisy 1 hz signal. As you can see the image, the signal is very noisy. I need its average amplitude peak value. However i can easily and perfectly find its frequency from FFT plot (i can find it after some smoothing algorithm). My aim is to reach average peak amplitude of this periodic signal. So can i extract peak amplitude value by using maximum amplitude of FFT plot? If yes, how? Inverse FFT? Thanks a lot, Cem