English question (perposition)

because oversea is adverb,if the word is adverb,no need to add any word in front of this word and adverb should put to the back of the sentense.that it...............
I hope I can help you...............

The preposition "in" is required when you mention a place.

唔洗....
in 係用 when u r talking about one particular place...
like....The parts are manufactured in China.