This may help some. These are pictures of the back of the instrument module removed from the bike. At least if you are trying to reach around and do it blind, you will have an idea of what you are doing.
Back of the speedo

Rubber cover plug removed

Carrier and rubber cap removed. The carrier is a bayonet mount, about 1/4 turn CCW to remove.

Bulb removed. It is a mini wedge. Pulls straight out.

Screenshot of CF Bulb chart from the Rattlebars schematic diagrams. Has bulb listed as a T-1 3/4, Mini Wedge. 74 or 70 bulb listed as replacement.
