Idiom
put someone out of its miseryput (someone/something) out of (their/its) misery
1.
to kill an animal or person because they are in extreme pain.
The horse's leg was badly broken, and the kindest thing was to put it out of its misery.Badly wounded himself, he put a gun in his buddy's hand and asked his friend to put him out of his misery.
2.
to end someone's worry or something's suffering.
I thought I'd call her with the test results today and put her out of her misery.Business was so bad, they considered bankruptcy to put the company out of its misery.