Editing text in confirmation window

Hi I am looking to change the text in the confirmation window after a booking. I know that when you hover over some of the writing an orange box appears and you can change it.
However some of the text that does not appear so I can not find a way to change it.

I need to change the ‘You already paid for this reservation’ as clients are not paying in advance.

Any help much appreciated
(ps. if you can write simple instructions that would really help me out)

Thanks

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