@telecoms-saganist-44 Warm welcome to the community 
Kindly spare a minute reading this which helps you to ask better questions in the forum 
From your statement I understand that you are trying to connect to H2 database using Postman.
Do you have any idea about the API’s for H2 database? We need API’s to connect the applications via Postman. Unless you are aware about the API’s or API documentation for H2 database there’s no possibility for the connection to the DB directly.
To get some more idea on it, there are public workspaces for some other DB’s. Please read through it 