Hi Helen,
from your question it is not completely clear what you have and what you really want. So I describe two cases.
First case:
You are having a .ods or .xlsx spread sheet document wanting to export it into an ASCII text file that looks like a table.
Choose “save as”, select file type .csv and give a new file name. Pressing “save” a pop-up window “Export of text files” appears. If you tick the box “fixed column width” on the lower left, the export function generates a .csv file which does not contain delimiters but pads your table with blanks to the respective appropriate fixed width column size. Rename the resulting file to .txt you are done. (You may import this text file into Calc at any time using the fixed width feature for importing .csv text files into a sheet.) Be careful, only the current sheet will be exported to your text file.
Second case:
You already have a csv file containing delimiters and text “” marks. Open this file with LO and use the appropriate import settings to get a nicely shaped sheet from your .csv table. If you now would try to save it immediately as text again, the “Export of text files” pop-up does not appear, because the file is already in text format. So save it as .ods file (convert it to .ods format) first and then save again as .csv. Now the description for the first case should apply.
Hope I met your problem.
Karl