Renovar means "to renew" or "to renovate". It's a great vocabulary word that can be used for anything from renewing a subscription to renovating a house.
In "Contrato", Maluma uses it in a romantic context. He sings "Quiero empezar de cero, olvidarnos de to' y renovar el contrato" (I want to start from zero, forget everything and renew the contract), using a business term as a metaphor for restarting their relationship. It's a clever and modern way to talk about getting back together.
Ever been so stuck on an ex that you can't even enjoy a night out? That's exactly where Maluma is in this song. He opens by saying, "Hace tiempo yo no sé de ti" (It's been a while since I've heard from you), and admits that even when he's at the club, he's just bored and thinking about her. He's trying to move on, but he's failing badly, looking for her "en los labios de toditas mis parceras" (in the lips of all my female friends).
He's heard from his ex's mom that she's seeing other guys to get over him, but he's not having it. Instead of giving up, he makes a business-like proposal: "Quiero empezar de cero / Olvidarnos de to' y renovar el contrato" (I want to start from zero / Forget everything and renew the contract). He claims that if anyone's seen him partying, it was only because he was looking for her. It's a classic case of someone who can't let go, trying one last time to win his ex back.