Help moving from PHP Version 5.4 to 7.4

HELP! We are a volunteer-driven not-for-profit offering motorcycle safety training and skill development with a huge database issue as described below. We cannot identify any of our volunteers that can tackle our database issue...here it is, can you volunteer your time to help us? We would be glad to hear from interns who need hours:

*Our custom-made education database frontend was created utilizing PHP version 5.4 and connected to a SQL server.

GoDaddy moved the SQL information and the webpages to an updated server, currently utilizing PHP 5.6.

My issue now is that the code is not allowing access to the information due to the differences in the PHP versions. Login errors. Depreciated calls, etc.

I understand it would be best to move up to PHP 7.4 minimally so this issue does not occur again soon.

We are in need of someone that can take our older code and freshen it up to work with a newer version of PHP.*

Please respond at your earliest convenience. We are a month into this and it has literally stopped us from performing important tasks to support our program. Thank you in advance for your consideration.