What to do if (somehow involuntarily) one kills an animal?

It happened to me during dinner, yesterday: I wanted to move a mosquito that was in my plate and accidentally killed it :( What's the appropriate thing to do in such cases? Is there any mantra to recite in order to have some benefit for the insect? I'm asking this because I read about a mantra to be recited "in front of your shoes" so that, in case of walking on top of an animal, then it would be "less bad". But probably I'm totally wrong :) In any case, I don't think my question is a duplicate of the guy who killed a mosquito on purpose because it was suffering. I killed it because my intention was to move it from my plate, but I didn't pay much attention and did it wrongly.