Enzo,
I hope this does it for you.
Here's a small part of the voice list from page 5 of the DGX-650 "data list" manual downloaded from Yamaha downloads.

Let's say I want to use the "MIDI grand piano" listed as voice number 8.
Reading across from the "8" I see Bank Select MSB = 0, Bank select LSB = 112, Program Change = 3.

So, in Anvil Studio I open the Event List, mouse click to get the tiny pointer on the extreme left in the right position,
then use the menu item "Edit" then "Insert MIDI Event".
With "Include all controller events" ticked, first selec "0: Bank Sel", choose the channel you want to set up, and (according to the table in the manual) enter the value of "0".
Press okay.
Then repeat the insert event but this time choose "32: BankSel LSB". Same channel but this time "112" (according tot the manual).
Lastly insert event again and choose "Program Change" then "change" the program to "3" (according to the manual).
When these are inserted the odd thing is that the inserted change will read "value 2".
That's correct. The values stored is always 1 less than in the table of Programs. (A MIDI quirk!)
It should look like this.

Hope that does it.
John.