Based on what best I understand you question, I am suggesting a solution. Give it a try.
Sample Excel Sheet has data in Row 1 & 2. Column C has date in valid Excel date format say mm/dd/yyyy. Note that in case your date is not in valid Excel format and is stored as just plain Text, a slightly different approach would be required.
Now in last cell say in E1 put the following formula.
=CONCATENATE(TEXT(C1,"dd"),"/",TEXT(C1,"mm"),"/",TEXT(C1,"YY"))
Now copy this column elsewhere as Paste Values Only. Say in Column F and clear column E
Clear Entries from original date column say C.
Set the Format of the Column to Text
Copy the temporary date Column F and paste special values into original Column C & clear F
Save the File as CSV.
![enter image description here](https://cdn.statically.io/img/i.sstatic.net/jbyvS.png)
Sample CVS how it looks now. Note that this is just a sample, original column C is not cleared for the time being. See the last column.
![enter image description here](https://cdn.statically.io/img/i.sstatic.net/nbJXm.png)
Update
In case CSV when opening back in Excel automatically converts date to default date format, then use this formula instead and check. However this method may affect behavior in any third party application expecting to import CSV.
=CONCATENATE("=",CHAR(34),TEXT(C1,"dd"),"/",TEXT(C1,"mm"),"/",TEXT(C1,"YY"),CHAR(34))
.qif
file before importing it? Is the date proper there? Is it preceded by aD
? Perhaps the problem is with csv>qif converter?