Go to https://peakmonsters.com/@yourusername/cards

Tick the box to only search cards "for rent" under Other. Then Click the Rotation Icon next to the card name. Now, go up to the Shopping Card, select how many days you want to renew, and pay.

This only works if the rental is still active, which should be the case if you are doing it within the 24h block the card was rented.