Hi Babette,
Multi pads can be recorded in real time on the keyboard using the 'Multi Pad Creator' function.
You access this on a Tyros3 by pressing 'Digital Recording' button and then pressing button C.
The voice that is used for recording the MP is the one currently loaded in the Right1 voice part, and you should be able to select your UVN for this, either before opening MP Creator or from within it.
Note that the voice can't be an S.Art., S.Art.2, or an Organ Flute voice, and if your UVN is one of these types, then when you record the MP in MP Creator, it will be replaced with a piano voice! Also note that if you want the MP that you make to follow the chords that you play, you need to use only certain notes!
You can find instructions on the procedure for actually recording the MP in the 'Tyros3 Reference Manual' which you can download if you haven't already done so. This is a different manual to the 'Owner's Manual' that is usually supplied with the keyboard.
I'm not sure where you are (other than in Europe), but the Reference Manual is available in a few different languages including French and German if that is better for you.
Here is a link to the Yamaha UK web page from where you can download it, there will be an equivalent page on your own local Yamaha site if you prefer...
https://uk.yamaha.com/en/products/contents/keyboards/downloads/manuals/index.html?l=en&c=keyboards&k=tyros3 The instructions for recording your own MPs are at the start of the section 'Multi Pads – Adding Musical Phrases to Your Performance –' which starts on page 70 of the English version.
Regards
Ian