detroit marine diesel engine v6 71 two sroke

hi there we have on one engine blue / white smoke at exhaust,
What to do?

can any body help me

You need to post more information.

Blue smoke is oil being burned in the cylinder. Usual causes are piston rings and or valve guides.
White "smoke" is not really smoke. It would either be water vapor (steam) or unburned, atomized diesel fuel.
My bet in this case it that it is unburned diesel. Why do I say that? Because of the blue smoke. It sounds as if you are losing or have lost compression and oil control in one or more cylinders.

I agree with Chris. You don't even give an indication of the severity of the smoking. A lot? A little bit? Engine cold? Engine warmed up? Both?

If the engine has a lot of hours, then it may be time for an overhaul. If the engine has low hours since overhaul, then complete diagnostics are in order to identify and pinpoint the cause and cylinders. If the engine has JUST been overhauled, it may need to be run for awhile to see if the smoke doesn't improve.