I believe the little holder loop
you mention is properly called the front brake cable clip
. It is number 11
in the parts diagram below.
It is 2 pieces that snap together. Old plastic gets brittle so it might break when you try to separate them to snap it around the new cable.
This piece is not necessary for riding your CT90. It just holds the cables neatly. There were originally 3 cable clips. They keep the cables from flapping when you ride.
You can use a ziptie or piece of black electrical tape to secure the cable if you feel there is too much slack.