"用木板遮住" can be translated into English as "cover with wooden boards" or "block off with planks", depending on the context and the degree of formality.
"Cover with wooden boards" is a straightforward and commonly used expression, suitable for most situations where you need to describe the action of hiding or protecting something by placing wooden boards over it.
"Block off with planks" is slightly more specific and might be used when emphasizing the act of completely obstructing or sealing off an area using planks (which are a type of wooden board).
In most casual or general contexts, "cover with wooden boards" would be the most appropriate choice.