Bongo 6 Bass Neck Won't Adjust

I have a Bongo 6 HS. In “Deep Purple”. Love the bass – but that wheel won’t turn. Thus I have too much forward bow.

What makes it more difficult is that the size of the wheel is smaller than the one used on my 5 strings. That makes the hole in it smaller and I can’t use as strong a tool.

I am using the strings that came with it. I am looking for strings with less tension.

Is there a fix for the neck issue?

Thanks

– Ziggy –