There are various approaches possible like Manual, VBA, Formula etc..But, I think most straightforward is following –
1. Save the file as Text (tab delimited).
2. Open the file in Notepad and copy the entire space between two values. (See, highlighted section between two values as in below picture)
3. Now CTRL+H and in Find What: box, Paste the space which you copied in step 2. And in Replace With: box put ; (semi colon)
4. Replace All, save.
5. Change .txt filename to .CSV