In the Note Game mode click on the button that displays the name of the current bass guitar tuning.

 
 
 
 
 
 
 
 
Initial, there is only the Standard bass guitar tuning in the list. The Standard bass guitar tuning can not be modified or deleted.
The fist way:
1. Press and hold on the element "Standard" for opening the context menu of this item.
2. Select the option for creating a new bass guitar tuning.

 
 
 
 
 
 
 
 
The second way:
1. Click on the settings button.
2. Select the option for creating a new bass guitar tuning.

 
 
 
 
 
 
 
 
Edit and save data of the bass guitar tuning.

 
 
 
 
 
 
 
 
The new bass guitar tuning will appear in the list. Click on an element from the list to select that bass guitar tuning.