Iw ill close this, as I found a solution.
%----access all xy data-----
d = findall(gcf, '-property', 'xdata');
xydatas = arrayfun(@(h) get(h, {'xdata','ydata', 'type'}), d, 'Uniform', 0);
%----adress xy data-----
x1=xydatas{3, 1}{1, 1}' ;
y1=xydatas{3, 1}{1, 2}' ;
w=xydatas{3, 1}{1, 2}'-xydatas{2, 1}{1, 2}';
g=fittype('a*exp(-b*x)+c');
f=fit(x1,y1,g,'StartPoint',[1, 0.02, 0.5],'Weight',w);
hold on;
plot(f)