Combine various custom master tables into one master user

I have tree projects running in production with three different databases Postgres

that manage their users individually and the tables are below.

Control Panel -> Database: salesDB, Table: user_master (id, name), other_table1, ...

Talent Panel -> Database: talentDB, Table: employee_master (id, name), other_table2, ...

Buyer Panel -> Database: buyerDB, Table: buyer_master (id, name), other_table3, ...

Now I want to manage all users in one new table by creating a new database for the admin panel.

Example: Admin Panel -> Database: adminDB, Tables: user_master (id, name)

Question:

1) If I create a new user_master table, how do I manage the existing original user id that is in use?

If there is another way please suggest me.