If ONLY reverse is gone...The Reverse input clutches are toast or the Low/Reverse clutches are toast.
If Reverse & Second gear are gone....The Reaction Sun Shell is broke.
If it "Locks up/Binds up in reverse" (Wont roll freely in either direction on level ground) The forward clutches are not releasing.
There is no "reverse solenoid".
Rebuild is the only solution for ANY of these problems. A GM dealer would just install a Sunshell if it was broke
