In Export Letters of Credit scenario, Unlike the beneficiary, who is usually a corporate customer known to your bank, and the issuer, who is normally a bank identified as such in your system, the applicant of an L/C is usually a company domiciled abroad. As such you don't normally hold details of this particular party on your books.
Accordingly, you cannot select such parties from your static data; they need at first to be captured manually.
There are two ways to do this. In a separate transaction, you can add the party to your static data. This would allow you to select the party. The more simple way is to add the applicant directly in this transaction as a so-called temporary party.
To add a temporary party, click in the "+" icon becomes active for a registering a new temporary address.
the window opens the 'Create temp. applicant (APL)' panel, where you can capture all the data for the address.