Tex processing hyperTTS - replacement RegEX

I would like to add audio using hyperTTS to my cloze cards but I don’t know exactly how to use RegEX to set up replacement rules.

In particular, I have no idea how to access the match group to use it as a replacement.

Instead of creating an audio voicing, for example, {{c1::der}} , I would like it to process only the “der”.

I tried some common syntaxes e.g. using $1 but none worked, as you can see in the image attached.

Could someone please help me?