or to select randomly an appointment from the list an click “weiter” (next) if there is an appointment available.
Ah, so the problem is that you can not record the next steps, since they rarely happen 
I would suggest you do it this way:
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Check in a loop if there is a “No appointment available” message shown on the screen
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And if not, then play the alarm sound
Here is a related forum post for this:
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Wait for the logo to disappear - #5 by ulrich (visual check)
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Wait for the item to be present and proceed to the next step - #2 by ulrich
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Or use verify Element Present for a HTML-level check
or to select randomly an appointment from the list an click “weiter” (next) if there is an appointment available
That should be very easy to do once you are at this step. Or do you have a specfic question about this?
Since you have a screenshot of the next screen, you can also try to create the next steps already using the visual XClick command.