How to insert values without knowing field names

[VBOB]

I want to Insert Values into an existing record of an SQL table, without knowing the field names.
Normally I do the following :
"INSERT INTO tblA ([User],[Date]) VALUES ('A','B') WHERE <condition>"

....but in this instance I don't know the field names ([User],[Date]), I merely want to insert the values into the 2nd and 3rd fields.