I assume that your are wanting to do the conversions in Excel.
If you have, for example, your fluid ounce(US?) values in Column A starting at A2, in B2 type the following formula:-
=CONVERT(A2,"oz","l")*1000 and then drag it down as far as you need.
You'll notice that, once you type in this part of the formula:-
a dropdown will appear with various abbreviated measurement choices from which you can select. You will find "oz" for fluid ounces(US) but you won't find one for millilitres. So, the conversion needs to be done to litres first and then multiplied by 1000 (1000ml to 1lt.) to obtain the result. Hence, this part of the formula:-
The "oz" is the abbreviation for ounces(US) and "l" is the abbreviation for litres.
You can, of course, just Google your query and a conversion chart will be immediately presented for you to use.