Mend one's ways (6)
(Other definitions for repent that I've seen before include "lying on the ground" , "Show remorse" , "Feel regret/remorse" , "John the Baptist's cry" , "Be sorry for - . . . . . . ye sinners" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mend one's ways</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for reform that I've seen before include "Correct(ion of) abuses" , "Abandon evil practices" , "Show improvement" , "Mend one's ways" , "Removal of abuses" .)