APEX 19.1 Shuttle Item (Shuttle Controls)

I am working with a shuttle item that on the left queries a database table for all groups  available to a user. The right side returns a query on the same table showing the groups which are currently assigned to the user.

I can shuttle the items back and forth using the built-in shuttleControl buttons, then after everything is done use a “submit changes” button.

In this button I have code similar to:

declare

    tab apex_t_varchar2;   

begin    

    delete from TECH_GROUPS

     where USER_ID  = :P30_SELECTED_USER_ID;

commit;

        tab := apex_string.split (:P30_GROUPS, ':');  

        for i in 1..tab.count loop