[GOWRISHANKAR]

i hve tried to change andriod marshmallow to oreo in coolpad note 3 . while that time in spf flash tool i unknowingly clickd format whole flash in format menu . thn i trid to install firmware of old marshmallow its is not installing

[X3non]

i hve tried to change andriod marshmallow to oreo in coolpad note 3 . while that time in spf flash tool i unknowingly clickd format whole flash in format menu . thn i trid to install firmware of old marshmallow its is not installing

did you take note of the build number of your CP note 3 device before attempting to flash the oreo rom?
and what error message do you get when you attempt to flash stock marshmallow rom? [attach screenshots]