Reverses
I believe the answer is:
undoes
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">reverses</span>' is the definition.<br/ ><span class="explanation-format__explanation">(undoing is a kind of reversing)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for undoes that I've seen before include "Loosens or ruins" , "Opens fastener or causes the ruin of" .)