Mehedi - if you want data1 to be used by your pushbutton3 callback, then just add this variable to the output parameter list of the function. So something like
function [data1,output_txt] = labeldtips(obj,event_obj,hdt)
dcs=hdt.DataCursors;
pos = get(dcs(1),'Position');
output_txt{1} = ['X: ', num2str(pos(1))];
output_txt{2} = ['Y: ', num2str(pos(2))];
data1=pos(2);
would do the trick. Call it from your callback as
function pushbutton3_Callback(hObject, eventdata, handles)
% do stuff
% call function
[data1,output_txt] = labeldtips(....);
