Hero Motocorp — mileage degrowing

Address:

501505

Dear sir I had given my bike for my 3rd servicing on 2nd November 2018. At Sri Sai automobiles hayath nagar RR district HYD pin code is 501505 . here the issue is
before this servicing my bike has giving millage is 62 - 65 kmts/liter but after this Servicing my bike millege is degrowing which is 54 kmts/liter what can I do sir ? What ever I want my bike previous millage.so pls resolve my problem as possible as.