Old STI 105 shift lever fell off Hello,

While riding home last night, my brake lever fell off. It's an older item on an older bike. What's the process to re-attached one of these?
You say you've lost some of the other bits.  This kills the brifter.

Seriously, just buy a replacement, probably you can find it used for $50.  Normally you'd redo the bar tape in order to replace the entire shifter, but if you want to avoid that, you could probably swap the entire internals of the new unit into the old body (I say probably because it may be a bit fiddly and perhaps not worth the trouble, and everyone needs new bar tape anyway!).