How to remove character format under .csv?

[Eric]

Does anyone have any suggestions on how to remove character format under .csv
file? For example, if I open abc.csv files, some text displays strange
character, because of missing fonts, but if I rename the file extention from
..csv into .txt, and then reopen abc.txt under excel, then all the text are
displayed properly.
Does anyone have any suggestions on how to remove character format without
renaming extention from .csv to .txt, then reopen it again?
Thanks in advance for any suggestions
Eric