410 Windscreen Wipers

[penman]

Hi
Hopefully an actual owner won't tell me Bristols are different.
You hinge up the cover over the spindle end of the arm,under this you will find a nut, undo the nut, lift the arm to its off the screen position to avoid the spring in the arm affecting what you do next.
Wiggle the spindle end of the arm about on the spindle till it is slack (this might need some sort of easing fluid WD40 or penetrating oil) as there will probably be some corrosion between the arm and the spindle (dissimilar metals).
Once the arm is off you will see it is mounted on a splined spindle, might be a tapered spline, or even a plain taper spindle.
Operate the wiper motor to make sure it has stopped in the proper self park position.
Then reposition the arm where you think it should be, spin nut down finger tight then foild the arm back down to check it is exactly where you want it, if necessary undo nut and reposition (trial and error) because it is always easier to move the arm when fold up away from the screen.
When satisfied tighten nut,
Might be worth while to take both arms off and check position of both while you are about it.

Have you ever inadvertently had the wiper motor going when ice has glued the blades down, or caught the blade with a sponge/brush while assisting the wipers to clear the screen?
That is what can often shift an arm on it's spindle whether it is a taper spline or a plain taper shaft.