Yamaha SY99 Owner's Manual page 86

For example to store your new voice in Internal memory bank C memory
number 16, press INTERNAL, then C then 16.
The voice will be stored into this memory
Press F8 (Stor), and the bottom line will ask "Are you sure ? (Yes or No)". If
you are sure you want to store the edited voice, press +1/YES and the bottom
line of the LCD will show "Store completed". If you decide not to store, press
-1/NO and the bottom line of the LCD will show "Store cancelled".
You will then return to voice play mode.
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