undo

Can someone help me to undo my seat belt?

有人能帮我解开安全带吗？

I did a really tough aerobics class and then went out for dinner and undid (all) the good work!

我上了一堂活动量很大的有氧健身课， 然后出去吃饭，结果所有的锻炼都白做了！