You can add the legend manually and set the color and marker as per your own. See the below example for your reference.
x = linspace(0,pi);
figure
plot(x, cos(x),'r')
hold on
plot(x, sin(x),'b')
plot(x, sin(2*x),'m')
qw{1} = plot(nan, 'r-o');
qw{2} = plot(nan, 'b--');
qw{3} = plot(nan, 'm-d');
qw{4} = plot(nan, 'k-d'); % You can add an extra element too
legend([qw{:}], {'Data1','Data2','Data3', 'Data4'}, 'location', 'best')
