Thank you for your post.
The question is "What do you want to happen?"
A field with 30 repetitions is actually one field with many values. Each repeating value is separated by ASCII (29). The information is available, but I'm not sure what you want to do with the SQL statement.
how can I duplicate that field with 30 repetition in SQL?
You should really ditch repeating fields and use a proper normalized system. Those records should be broken down into related records. You can do this by importing into a new table and it should give you the option to split the repeating fields into their own records.
True Data should never be stored in a repeating field. They make great utility tools but other than that, you should stick to relational theory.