If dipole moment is (qxd) charge x bond length then why HF has higher dipole moment(1.9) & HI 0.4 when the d value is shorter of HF?

This is because of very high electronegative value of fluorine. So the q vaue is quite high in this case which overcomes the increase in bond length in Case of HF.
So we should think about both the parameters ‘q’ and ‘d’ and product will give you the final result. We should also note that the dipolemoment of HCl is higher than the dipolemoment of HF. In this case, increase in bond length overcomes the charge difference and consequentely diploemoment inceases.