In the calling form:
DECLARE
pl_id PARAMLIST;
BEGIN
pl_id := get_parameter_list('temp');
IF NOT ID_NULL(pl_id) THEN
destroy_parameter_list(pl_id);
END IF;
pl_id := create_parameter_list('temp');
IF ID_NULL(pl_id) THEN
message('Opps!');
RAISE FORM_TRIGGER_FAILURE;
END IF;
add_parameter(pl_id, 'EMP_ID', TEXT_PARAMETER, :block.field);
open_form('form name', ACTIVE, NO_SESSION, no_share_library_data, pl_id);
go_form('form name');
IF NOT form_success THEN
message('Opps!');
RAISE FORM_TRIGGER_FAILURE;
END IF;
END;
In the called form create a parameter with the same name as above 'EMP_ID' in this case.
In the when-new-form-instance trigger write something like this:
BEGIN
IF

arameter.emp_id IS NOT NULL THEN
set_block_property('block name', DEFAULT_WHERE, 'emp_id = to_number

parameter.emp_id)');
END;
Hope you get the picture, else search for parameters in the Oracle forms builder help.