You cannot use Sales Navigator and bring that info to Andsend to obtain emails due to 2 reasons:
Andsend does not enrich the data that you upload
LinkedIn does not offer the option to export account and lead information from Sales Navigator into a CSV or XLS file. Read more about it here
However, there are alternative solutions available that complement Andsend exceptionally well. One such solution is Phantombuster. They specialize in extracting required information from pages such as LinkedIn and enhancing prospects by providing their email addresses.
Subsequently, you can import the list created through Phantombuster into Andsend to initiate your outreach.
Read more about the pricing at Phantombuster.