Double check that the provided user has expected permissions on the pluggable database.
Connect as oracle user on DB server and run the command to list the status of default Oracle listener :
to get a list of services registered to it.
Login to DB using OS authentication to root container and run query:
SQL> select name, pdb from v$services order by name;
From the result, you have ideas of existing Pluggable Databases(PDB) and their service name. If the service name is incorrect, proceed to change the service name in the installer UI.
Otherwise, double check that provided user can access Pluggable database created for UIM. If not recreate a local user for this database.
SQL> alter session set container = pdb_name;
SQL> create user uim identified by 123456 default tablespace uim;
Grant required permissions to such user according to Grant Permission
, cancel the installation and run the installer again providing this user name and its matching service name in installer UI.