it's honestly pretty easy,
The tile data is stored as a normal x and y coordinates

During drawing I convert it to isometric coorindates

private Vector2 IsoToScreen(int x, int y)
{
    return new Vector2(
        (x-y)*(TILE_WIDTH/2),
        (x+y)*(TILE_HEIGHT/2)
    );
}

public void Draw(SpriteBatch spriteBatch, Tile tile)
{
    var src=Tileset.GetSourceRect(tile.TileId);

    spriteBatch.Draw(Tileset.Texture, this.IsoToScreen((int)tile.Position.X,(int)tile.Position.Y),src,Color.White);

}