这个句子有误，可做如下修改：
1 If each person plays their part—even for just one meal a day—Hong Kong will be on its way to making considerable progress towards sustainable seafood consumption. 真实条件句。
2 If each person had played their part—even for just one meal a day—Hong Kong would already be on its way to making considerable progress towards sustainable seafood consumption. 错综时间虚拟条件句，从句为过去时间，主句为现在时间。
3 If each person should play their part—even for just one meal a day—Hong Kong would be on its way to making considerable progress towards sustainable seafood consumption. 虚拟条件句，主从句均为将来时间。
