Yamaha DDK-7 To erase all instruments:, To replace the instrument:

DDK-7 Owner’s Manual
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Rhythm Program
Select [CLEAR] to erase the selected instrument.
A bell sound indicates that the instrument has been erased.
The following method can also be used to erase one instrument.
While holding down the [CLEAR] button, press the key on the
keyboard corresponding to the instrument you wish to erase.
A bell sound indicates that the instrument has been erased.
To erase all instruments:
Press [CLEAR] in the display.
The following display appears, prompting confirmation of the operation.
Select [CLEAR ALL] to erase all instruments.
All instruments are instantly erased.
When you want to replace the instrument you have already entered with another
instrument, it’s not necessary to delete and re-enter. You can quickly replace the sound
with the following procedure.
To replace the instrument:
Before the operation, stop the rhythm.
Select the key to which the instrument you want to replace is
assigned.
The key name you have selected and its instrument name are displayed.
Simultaneously hold down the [CHANGE] button in the display
and press the key on the Upper or Lower keyboard that
corresponds to the instrument you want to use.
The instrument is instantly erased and replaced with the newly selected one.
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Instrument name
Selected key
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