Hi Terry,
To change MIDI events (notes, velocities, timing etc) you need to use the Step Editor, not the Channel Edit screen.
In order to select a specific channel to display in the Step Editor, you must first select it as the Recording channel from the Rec Channel screen.
However, many Yamaha Preset styles have most of their channels (other than Rhy2) locked for editing the existing patterns, and will only allow you to select one of them as the Rec Channel if you delete the existing data first!
I have just tried to edit a couple of DOO.DE styles in Genos Style Creator and they both did this too!
To edit such styles you need to make a copy of the style and then use a computer to either...
1] Try to 'unlock' the locked channels using a program such as Jørgen Sørensen's 'Style Unlocker' program (for PC) which sometimes can unlock style channels, but not always!
http://www.jososoft.dk/yamaha/software/stun/index.htmIf this works you can edit the style back on Genos as I described above.
Edit: I just used this program on one of the 'locked' DOO.DE styles, and back on Genos I can now select any style channel for editing (by arming it for recording! - you try working out Yamaha's logic!

) without getting the dreaded deletion warning!
2] Alternatively you could just edit the style on a computer using a program that doesn't care about Yamaha's restrictions and gives you access to all channels without any need to unlock them. Such a program is 'MixMaster' which was originally provided by Michael Bedesem but is now administered and developed by Etienne Volbragt.
https://psrtutorial.com/MB/mixMaster.htmlUnfortunately there is a bit of a learning curve to use the program, but for the type of simple edits that you referred to, it is quite straight forward.
3] You can use 'StyleMagic' to edit such styles as Pino suggested, but unlike MixMaster, StyleMagic is not free. Unless you think that you might make use of StyleMagic in future for other of it's many features, it may be somewhat overkill for your current requirements!
Regards
Ian