Importing a List but de-duplicating based on the Marketo Lead ID

I want to basically clean up some of the leads that didn't make it to our CRM because they didn't have the Last Name and or Company, those 2 fields are required for a lead to make it into our CRM from Marketo. So our intern went ahead and put in this information in an excel sheet, now when I import a list, can I use the Lead ID that Marketo provides to de-duplicate? In my smart list filters, the field is called ID, but when I search for it during an Import I can't seem to find it. Is it called something else? I had exported these when I took the list out for the intern to work on.