Extract data from matrix to list according to criteria

Hi everyone!

I'm creating a monthly schedule template for scheduling customer diaries as shown below.
Basically, I will insert with an "X" the day that the client has an appointment throughout the month.

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As I insert an "X" for a given customer on a certain date, I would like the customer's name and date to be automatically listed in another spreadsheet as shown below.
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Does anyone have any idea how to come up with this? I tried some combinations with OFFSET, INDEX, MATCH but without success.

Thanks in advance.