I presume you are talking about the small shaft which is actualy the gear change/clutch shaft.
If you move the engine in and out of gear you will see a small connector come into view thats fitted with a small pin or bolt. This must be disconnected before the bottom casting can be removed.
There are lots of variants, but an old DT75 should look something like below.
This link is very useful for looking how old Suzukis go together on Microfiche.