New Instrument in Library - sound?

Hello, I created a new instrument by duplicating an Alto Recorder and adjusting the transposition (I needed a Flauto dolce in Bb). So far, so good. But: when I use the new instrument, it plays back with the piano sound. I’d like the [GM Recorder] for this instrument too, as in the default Alto Recorder, for this and for future projects.
Any step-by-step help for me as a beginner in this field would be very welcome.

This is because the Playback Templates don’t know anything about your new instrument.

Generally, you would need to configure the playback manually for the new instrument. Save it as an Endpoint. Create a custom Playback Template that includes this new Endpoint together with your normal automatic endpoint.

If this is too much work, you could create your new instrument as a Variant of the Alto Recorder, rather than a duplicate. It will then inherit the sound settings, but will be harder to find in the Instrument selector(!)

Thank you Janus,

it took a while and some try and error, until I have figured it out now.
I called the Endpoint configuration “Flaut dous” and created a custom Playback Template by duplicating the Auto[matic] one, calling it “Flaut dous” and adding that Endpoint configuration to it.
It did not work - until I shifted the Endpoint configuration up onto the first list place:

Now I can apply this PT to any new project, where this flute in Bb is being used. I wonder when this will happen…

You already find out the solution, this section from the manual explains the ‘Why’

Entries

Contains a table of all the custom endpoint configurations and existing playback templates used by the selected custom playback template. Entries are listed in order of priority, meaning that Dorico Pro assigns sounds from the top entry first. We recommend that you always include a factory default playback template at the bottom of the list as a fallback to ensure that all instruments are assigned sounds.

Thanks a lot.
Yes it’s new terrain for me, and I only came across this once so far, when installing Cantai.