There are many modules that can do this. I would suggest Net::Works or NetAddr::IP. With Net::Works:
use v5.16;
use Net::Works::Network;
my $network = Net::Works::Network->new_from_string(
string => 'FE80:0202:B3FF:FE1E::/56' );
say $network->first;
This will output fe80:202:b3ff:fe00::
.