ושב ה’ אלוקיך את שבותך ורחמך…  (נצבים ל:ג) 

Dovid Hamelech says in Tehillim: “שובה ה’ את שבותנו” – Hashem shall return those who want to return (תהילים קלא:ז).  We ask Hashem since we do not have enough strength to do teshuvah (repent), Hashem should do teshuva for us. This is what the passuk alludes to, ושב ה’ אלוקיך – if you are serious about returning to Hashem and are willing to forsake all your sins, then את שבותך Hashem will, as if, repent for you, ורחמך – Hashem will have mercy on you and help you do teshuvah.