OK- I've found some free time to produce the procedure... Here it is...

Have Fun !!

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Initial setup
1. Press Program Menus > Control > Overall Touch Sensitivity.
2. Check that the After Touch Settings are as follows : ON/OFF set to ON : Curve set to 10 : Treshold set to 1.
3. If these settings need to be changed, then adjust as necessary.
4. Press EXIT x3 to return to the Home Screen.
5. Make sure only RIGHT1 is selected in the Part Select option buttons.

Procedure
1. Press Sound Explorer > Brass > select either Trumpet NV or Solo Trumpet NV (to your taste)
2. Press Program Menus > Sound Edit > Tone. You should see under Tone Name, Trumpet if you selected Trumpet NV, or Brt. Trumpet 1 if you selected Solo Trumpet NV
3. Press EXIT once to return to the Sound Edit Menu screen.
4. Press Controller and select After Touch (fourth button from top, on left of screen) Orange rectangle will move to After touch.
5. Check that in the Function Column, LFO 1 Depth is selected.
6. Lightly, Press any Note key (within normal Trumpet range) and you should hear the Non-Vibrato Trumpet sound.
7. Press the Note key harder and use the UP Arrow / Down Arrow buttons at the bottom of the screen, in the Depth Column, to adjust the Vibrato Depth to your liking - around 45 seems like a good starting value.....
8. The Vibrato initial Speed appears to be set to 21, however, you can change it to your liking as follows.
9. Press EXIT once to return to the Sound Edit Menu screen.
10. Press LFO and you should see the Pitch Modulation screen. Note that only the 1st voice is ON.
11. Check that LFO 1 is selected (Default). You can now adjust the Vibrato Speed (Default 21), using the Up Arrow / Down Arrow buttons at the bottom of the screen, under the Speed Column. Leave all the other parameters at their default settings
12. Having adjusted the LFO 1 Speed, you may wish to re-adjust the LFO 1 Depth... Press EXIT once and then follow the procedure from step 4 above, repeating as necessary, until you are satisfied with the Depth and Speed results.....
13. Press Program Menus to return to the home screen.

Save Your New Sound
1. Press Program Menus > Sound Edit > WRITE > Sound Naming > CLR
2. Give your New Sound an appropriate name - for example "TouchVibTrumpet" and press OK.
3. Select a Memory Bank location for storing the new Sound and press OK - Your New Sound will be available in the MEMORY button in the Sound Group.
4. It would be a good idea to now Save your entire Sound Memory to a new location on your SD Card
5. On Page 2 of 3 in the SD Save screen, select 'All Off' and then select only the SOUND MEMORY option and name the file appropriately - say New Trumpets......

Additional comments.
Using this method for adding Vibrato to a sound, you can choose when YOU wish to add the effect by just pressing harder on a Note key. You can even play a Note without Vibrato, then add the Vibrato using After Touch and return to a Non-Vibrato sound by just gently releasing the After Touch pressure.
The effect can also be added to other Brass instruments - such as Trombone, Muted Trumpet, Flugel Horn etc. or even Sax and Flutes, by selecting the appropriate NV version of the instrument in Step 1 of the procedure above.