Database connection and modification

First of all may I know, how I can connect to the database after I run my exchange?

Is it possible for me to change the database schema and add certain data for users. In my case I need to make certain changes to make it accepted for regulators and it requires user information but it is different than what is provided in the kit. So I am wondering about changes and customization there.

You absolutely can. In Kit 1.3 we will add the database folder that makes it super clear on the database models, migrations etc. You technically can then use that and customize your exchange the way you want. Take a look at some examples in plugins where database operations and commonly used.
If you have a specific example in mind, you can bring it up here for further assistance.

As of today April 2nd 2020, we have db folder in he hollaex kit and all db models and migrations can be seen there. I hope this helps you with your db customizations.