Upgrade php version from 7.4.33 to 8.0.26

Ref: Upgrade to version 8.0.26 php
Plugin: Extended Random Number Generator

7.4.33 of the plugin is working OK. I got the below error when I upgrade to version 8.0.26 php.
==================================================================================

Warning: Undefined variable $menu in www/xxxxx.ca/wp-content/plugins/extended-random-number-generator/random_number_generator.php on line 62

Warning: Undefined array key “page” in www/xxxxx.ca/wp-content/plugins/extended-random-number-generator/random_number_generator.php on line 305

Warning: Cannot modify header information – headers already sent by (output started at www/xxxxx.ca/wp-content/plugins/extended-random-number-generator/random_number_generator.php:62) in www/xxxxx.ca/wp-admin/includes/misc.php on line 1416

Warning: Cannot modify header information – headers already sent by (output started at www/xxxxx.ca/wp-content/plugins/extended-random-number-generator/random_number_generator.php:62) in www/xxxxx.ca/wp-includes/functions.php on line 6865

Warning: Cannot modify header information – headers already sent by (output started at www/xxxxx.ca/wp-content/plugins/extended-random-number-generator/random_number_generator.php:62) in www/xxxxx.ca/wp-admin/admin-header.php on line 9

==================================================================================
Can you help me to fix the plugin?

Thank you for your help and assistance.

Best regards
Dominic Ko