When you set a new capped IO without an expiration date, your remaining amount will start decreasing based on the activity of your campaign. If you add a new capped IO, it will be merged with the existing one and both total and remaining amounts will increase.
i.e. if you have initially set up a £14,677 capped IO without auto-renew on, your available budget will start decreasing based on your campaign activity.
However, if you choose to create an additional capped IO of £5,000, your existing capped IO will be updated and remaining amounts will increase by £5,000, making the total IO budget £19,677.