After installing PostgreSQL, run this command in terminal to install PgAdmin4 on Ubuntu,
sudo apt install pgadmin4 pgadmin4-apache2 -y
During installation, it will ask for Email Address and Password to access. Give any email address that will be used as username and Password that will be used to access admin panel.
After that you can access pgadmin4 by entering: localhost/pgadmin4/ in web browser.
Now you may need to configure your postgreSQL manually. To do that, click on Server and create a new server. Give it a name and click on the 2nd tab of server form. Give relevant information i.e. IP Address of server where postgreSQL is hosted and the Port no of course. Have a look at other options as well.
Your PostgreSQL database will be configured with newly installed pgadmin4 as well.