Help is greatly needed with page processing in APEX

Question

hello everyone please could someone help me with a survey application that im working on . Basically i have  a page that has 5 different regions on it an each region has a LOV which has the following display values ( agree, strongly agree, disagree and strongly disagree)  then return values for these are 20 , 50 , 10 and 5 respectively and this is the select from statement to create the LOV below and the table used
select EVAL_OPTION as display_value, FRM1_REG1 as return_value
from REL_DIM_SC_TBL
order by 1
The LOVs work fine . However when i tried to insert the inputs from the users into another table by means of a page process im getting a error that i cant seem to resolve my tables are :
REL_DIM_SC_TBL   -- where the display data for the LOV's come from
REL_DIM_SC_IMP   -- is the table that where the values that the user has selected is stored
The page items are set up as follows :
   Relationship Dimension Scoring
JOE  Logout
WELCOME
  so where you see welcome above is a text field above the regions where the LOV's are and used the select :app_user from dual ; to populate it because in order to insert the data select by the LOV's on the page there has to be an item with a primary key . Which is what i wanted was for the current user using the app to be inserted into the REL_DIM_SC_IMP table . But when i click the submit button i get an error
below is the select of the automatic DML action i set up under page processing    
Name
Page:
3 Relationship Dimension Scoring
*Name (Value Required)
Type:
Automatic Row Processing (DML)
Process Point
*Sequence (Value Required)
Process Point
Run Process
Source: Automatic Row Processing (DML)
*Table Owner (Value Required)
*Table Name (Value Required)
*Item Containing Primary Key Column Value (Value Required)
*Primary Key Column (Value Required)
Item Containing Secondary Key Column Value
Please guys i have been stuck with this for a long time any help at all will be greatly appreciated

Answer 1

Hello Krunal thanks so much for your reply i did manage to sort out that error how ever there is an other one that im stuck with . Basical i have a table with 6 columns begin score1, score2, score3, score4, form_total, User_id
What i want to do is create a trigger that adds the four  numeric columns into the form_total
the trigger syntax i used was
create or replace trigger "Score_Total_t1"
AFTER
insert on "Score_Total"
for each row
begin
:NEW.USER_ID := ('APP_USER');
:NEW.form_total := ('Score1' + 'Score2 '+ 'Score3' + 'Score4 ');
end;
However the :New.USER_ID works fine to input  the currrent user but im getting an error with :NEW.form_total
Any ideas would be greatly appreciated
thank you