IIRC – you undo the 5mm Allen bolt at the top that threads into the elbow, and if the elbow is really tight you can use a 10mm spanner (on the flats) to move it (you can also use the spanner to hold the elbow in place whilst you re-tighten the 5mm Allen bolt)
The elbow isn’t fixed, it might just be really tight in there! I think they were a pretty tight interference fit to stop them moving when braking.
I had a set of HS33 race lines on my trials bike circa ‘97, and that worked for me!
A