Case else using and insert statement to capture rows

Good Morning,

Would someone be kind enough to look at this code? I can’t seem to get it to work.  The scenario is is that I have a column named   date_time  that was data typed as varchar2 when created in one of our tables.   The etl downloads into this column any information that has a date format in it along with other information not realated to date type. This is the reason I chose to use the regexpr_substr to search for and strip out the date string alone. There are 18.5 million rows of which I was able to identify 3.8 million rows that are not null.