#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my @account = qw( 96329XY 7776fc 334457yg 2233oop 000001 8877666b);
my @file =  qw(8877666b.txt 2233oop.txt 334457yg.txt 7776fc.txt 96329XY_K.txt);

my %seen;

for my $acc (@account) {

   next unless $acc =~ /^\d+/;
   my $key = $acc;
   
   push @{$seen{$key}}, $acc;
}

#print Dumper %seen;

for my $filename (@file) {

   next unless $filename =~ /^\d+/;
   my $key = $filename;
   ...
}