Upgrade/fix a Laravel application from php5.6 to php7.4 and above

I have an application running as localhost xampp. It was working fine with php5.6. However I cannot use it now because my xampp has php7.4 and above. I am having errors such "Function mcrypt_get_iv_size() is deprecated"
Let me know if you have question, comments or suggestions. I automated and generic responses will be ignored.