Convolution Theorem: Hamming Window on a Time Series and Fourier Domain
Fistly, you need to pad the data (y) and the filter (Hamming window). The minimum required length to avoid circular convolution = data length + filter length - 1. In this case, it is 100 + 7 - 1 = 106. For convenient, you may choose power of 2 length, in this case 128.

So, pad the data to 128, do fft on it.

Pad the filter to 128, do fft on it.

Multiply both ffts.

Do ifft.