Hello Jerin,
I tried to recreate the attribute with the same id and name and got duplicate id error, then I deleted the error entry from the df_custom_attributes table and restart services and the attibute dissapeared from the project attribute list in studio.
I had a second attribute in error, deleted from the table and then tried just flushing System Caches without restarting and the attribute also gone from Studio.
Thanks a lot for your answer.