SQL & PL/SQL :: Create Block Of Code That Would Search In All Tables In Schema For Column_name

I want to create a block of code that would search in all tables in a schema for a column_name where its data_length is like 4000 let's say. This data_length is actually dedicated for a comment column. If found, all not null column with like 4000 data_length will be changed by string "Comment has been removed". I have the following script below but it seemed lacking.

begin
for rec in (select table_name, column_name from user_tab_columns where column_name like ?data_length? = 4000 order by 1,2) loop
begin
execute immediate 'update '||rec.table_name||' set '||rec.column_name||' = ''Comment has been removed'' where '||rec.column_name||' is not null';
commit;
[code]........