Pass it through

sed 's/^[^:]*: *//'

This sed substitution will delete everything from the beginning of the line up to and including the first : and any spaces after it.

Pass it through

sed 's/^[^:]*: *//'

This sed substitution will delete everything from the beginning of the line up to and including the first : and any spaces after it.

If you have the string in a shell variable $a then

printf -- '-%s\n' "${a#*-}"

This uses the parameter expansion ${parameter#word} to delete everything up to and including the first -. The dash is inserted again by the printf. This does not use any external utilities when run in most modern shells.