Applying bandpass around my signal

Hello,

I'm trying to apply a bandpass around freq 0 without luck. I'd be happy to receive some help please

 x=scan11(1,:)*1e-3/3e8; y=scan11(2,:);
plot(x,y) %my function

[XX,ff]=trans_fourier(y,mean(diff(x)));
plot(ff,abs(XX)) %gives the Fourier transform

I want to choose the freq around 0. let's suppose -1e13 till 1e13 and than to make ifft and to plot the signal after this filer.

How should I start doing this? the command

YY=bandpass(y,[-1e13 1e13],1/mean(diff(x)))

didn't help here unfortunately.