Switch My BMW740il changes from automatic to manual by itself . can you help me?

On the gearbox n/s u will see a cable that moves it from park etc.
when this twist just a little it thinks u r moving the stick across.
if u undo the 13mm nut and turn just a liitle bit tighten it.
check your speedo cluster that the gear it says is correct to what gear stick says, if not adjust again until correct.
i had this problem myself and this was the case after i fitted a engine, engine and box has to come out.