If the one character you both sent is correct, you should have the numbers "9" and "0".

"9" would represent the 2-letter combinations "NI" and "NE", while "0" would represent "ZE" and "RO".
Don't forget to flip each of the two-letter combinations.
Look for the 4 squares in the chart that have these 2-letter combinations.

Read the words in those 4 squares from top to bottom, and you will get the clue for the final password.

You will know the password by saying out the 4 words: "Sink", "Crow", "Knee", "City".

It helps to say them fast!