LTspice FFT magnitude unit conversion question

Hi,

    I am working with the 'View -> FFT' function of LTspice, it says ' Fourier components are normalized to correspond to the time domain RMS amplitude', which I don't quite understand the math behind this statement and the magnitude of the FFT result is 'dB' by default.

   I am doing some conducted EMI simulation, which should have unit of 'dBuV' ( dB micro volt), so I am wandering how can I convert the default 'dB' into 'dBuV'. (I am doing this with MATLAB, I exported the FFT result in 'Real, Imaginary' form, I need equation to do the conversion).

   Could anyone help me on this problem? Thank you!