Use a hash for your identifiers. What you did is not perl :(

Here's minimal changes to make it (sort of) work.

#!/usr/bin/perl

# https://perlmonks.org/?node_id=1222918

use strict;
use warnings;
use Tk;

my @meals;
my %identifiers;

my $mf = MainWindow->new;

for (my $j = 1; $j < 7; $j++) {
        my $frame = $mf->Frame(-background => 'alice blue', -padx => 2
+0, -pady => 5)
                ->pack(-expand => 1, -fill => 'both', -side => 'top');
            $frame->Label(-text => $meals[$j-1], 
                        -background => 'alice blue', 
                        -width => 9)
                ->pack(-side => 'left');
            $frame->Text(-height => 6, 
                        -background => 'white', 
                        -width => 25)
                ->pack(-side => 'left');
                
            my $c = 0;
            for (my $i = 2; $i < 9; $i++) {
                if ($c <= 6) {++$c;}
                else {$c = 1;}
                    my $id = $j . $c; # Create identifier
                    $identifiers{$id} = $frame->Text(-height => 6,
                                -background => 'white', 
                                -width => 10)
                        ->pack(-side => 'left');
                } #end for $i
        } # End for $j

$identifiers{'22'}->insert('end', 'R2, C4');

MainLoop;
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