I had the same problem and was on this site reading the steps. It looks like the person who wrote the solution missed a step. So I am going to lay it out properly.
When you first open Total Commander you will see your directory panel.
If you have both panels open you will see two sides.
You want to look down at the bottom of the left side of the panel.
You should see a + button. Upon clicking on the + button a new window will open that says Add/Edit button.
There will be five options.
Function Type will be the first one at the top.
You should see an arrow pointing down on the far right side of the window.
Click on the arrow pointing down.
A drop down menu will appear.
Click on view file with app.
Under Function Type you will see View file with app appear.
The next option is Command: To the far right of the window you will see >> to right arrows.
Click on the double right arrows.
A window will open that says Choose app.
Scroll down and find TotalCmd (Queue)
Click on TotalCmd (Queue)
The next option below is Parameters it should now say file:%P%N
Click on the parameters line and clear this information. You can also just highlight the text and cut it.
The next option is Icon (click to change) if you want to change what the button is click on the icon .
A new window will open that says Open File.
You can open a image fille if you like, or click on installed apps if you wish to use an icon associated with another app.
The next and final option is OK/APPLY.
When you are satisfied with your new button click on OK/APPLY.
You have just created your first button. You should see the new button to the left of the + button.
If you need to change the button simply long press the button and a drop down menu will appear.
Click on properties and you will be able to edit the button.
I hope this helps. Enjoy