This is a broad question, so here is a broad suggestion. You might need to iterate through the records in your table with a python client, and parse the strings in each column for valid urls, using either a regular expression or some other python parsing library.
Once you find matches for a column or record, you could set them to another column
URL_found with some kind of delimiter between urls...but it would seem to be more useful to create a new db table like
URL_found with foreign key relations to the records in this original table.