Due to project restructuring, his tasks were re-assigned to the new team.

re-assigned 是动词 re-assign 的过去分词形式，在句中表示被动。re- 是前缀，表示"再次、重新"；assign 是动词，意思是"分配、指派"。re-assigned 合起来表示"被重新分配"的意思。