Cashback can be redeemed by admins or business owners on your company Ramp dashboard. Additionally, admins and bookkeepers are able to view your company's earned cashback and redeemed cashback amounts in every statement.
Head to your business overview page and click on 'Payments', then click on 'Manual Payment' to redeem the cashback. From there, you can generate a payment to Ramp to apply your cashback to your existing balance by using the bottom 'Cash Back' section. Note that your cashback will continue to accrue over time, and will not expire.