Problem with a cube

Hello everyone !

Firstly, excuse me if I did something wrong in my post, I am not used to using the Internet because of my age (my grandson found this website and created the account for me).

I have a puzzle given by a friend of mine to solve (without his help) but I am stuck.

It is a 6x6 cube (a cube with 36 little squares on each side). On each little square, there is a symbol (these are symbols we invented together, only the two of us know what they represent : a letter, two letters, a figure, punctuation, etc.). So far, I have managed to solve half of the puzzle.
The first part consists in sequences of triplets like EBD with E the side and BD the coordinates of the square on the side. Thanks to this, I have an encrypted sentence.

My friend only told me that the second part, the part I have troubles with, is the key to decrypt the sentence. There are sequences of couples. Each couple is composed by a letter and a figure like C1 or E2. Those couples are supposed to point one of the 216 little squares of the cube but I don't know how.

I thought that maybe I could study the net of the cube so that I have something in 2D but it led to nothing. Maybe my idea of studying the net of the cube is good but my method is wrong.
I am running out of ideas...

Would any of you have a suggestion about how I could use these couples to identify the correct square ?

P.S. : I am sorry if this is unclear or if my question is not asked on the good section. I am not very good with the Internet...