What else can I do to make it start up

I have a 2007 Dodge Magnum 2.7 engine that was
mixing oil and antifreeze let it sit for 6 months and
just bought a 2005 Chrysler 300 2.7 engine took
the car to the shop and took the engine out of the
Chrysler I put it into the Magnum the engine was
running in the Chrysler but now that it's in the
Magnum that won't start up what can I do the
mechanic told me I need to reprogram the
computer is that true