Chony,
1) Left Hold is not an assignable Tyros 4 foot controller function option.
2) I also am not able to find the "Left Hold" on/off included anywhere in the Yamaha Tyros 4 Data List manual
as a triggerable midi command (or via SysEx), so assume it's not supported other than by actually physically pressing the left hold button itself.
That said, the Left Hold on/off status is storeable in Registration and included in the 'style' group of Reg Memory Contents.
Be sure that the STYLE box in 'Reg Memory contents' (memory button) is checked.
Here's a (albeit 2 pedal) WORK AROUND SOLUTION for you:
Create via: Function > Registration Sequence
Two adjacent registrations (Reg 1 to Left Hold on, and Reg 2 to left hold off, and subsequently assigning one pedal to 'REG+' and the other to 'REG-'. After you create this REG Seq you should be able to switch back and forth between the Left Hold on/off status settings via the 2 assigned pedals.
Hope this helps. - Scott
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