The files visible and available for Import are determined by the settings within Importer. The description below refers to Nominal Journals but the principle is also applicable to other imports.
Open Importer
Select <Company Name>, Import
Select Nominal Ledger
Select Options, Definable File Names
Against the the field entry for "From File", enter *.TXT (If you only use .CSV for import files you might wish to change this to *.CSV)
Click OK
Check the box adjacent to Journals under From File :-
Configure the other settings as required
Click OK - this will then ask for a number of confirmations
When the Import File dialog box opens it will now show only the types of file specified at step 5 above