'He went on to kohl it [namely, rim the eye with kohl], so he/she blinded it [the eye].'
This is a rough translation of the Arabic idiom, 'ذهب ليكحلها فعماها'
To rim the eye with kohl is to beautify it. It means trying to fix something and then making it a whole lot worse. It's not the same as 'He added more water to the clay', which in English would be 'add insult to injury'. It's different.
Is there a similarly colourful idiom for this Arabic expression in English?