For your question, we would like to have below suggestion
Normally, materials imported for manufacturing products exported out of Vietnam shall be declared in two modes:
1. Declaration mode of imported materials for manufacturing goods exported
2. Declaration mode of imported materials for carrying out processing Contract with foreign trader.
Basing on nature of your trade transaction, the materials shall be declared customs in mode no.1 or no.2. For detail of customs procedure, you should refer to chapter I part II and Article 32 of Circ ular no.194/2010/TT-BTC on December.06th.2010 by the Ministry of Finance, guiding customs procedures, customs inspection and supervision, import duty, export duty and tax administration applicable to imports and exports.