Get data from DB and show in customer portal when creating a ticket

I am new in Jira development and need an advice for solving this problem:

I need to have a custom filed, which should be auto filled with Reporter’s manager’s username. The manager’s username is kept in other SQL DB. I need to show the custom filed with already filled in information before a ticket is created, so that a customer is able to change his/her manager’s username, in case the manager is on vacation.

Please help with a good advice to achieve this goal

Will the user be able to fill in the manager’s username by typing it or by choosing the corresponding username as an option from a list of suggestions?

Hi, Did you get the solution for this problem.

Thank you.