Through the menus, in my opinion there are chaotically placed buttons for index settting. For example on the main menu for character formating (button with a framed A leads here), the buttons are on the bottom of the function list. While in the submenu with font styles, the are the buttons placed next to the button for increasing and decreasing font size, which I think is the most logic possition. 1) open any text document 2) on the botton right corner tap on the edit button 3) tap on the button whith framed A 4) go through all submenus 5) you will see differenct positions of buttons for index setting between the submenus System information: OS: Android Device: Lenovo TB-7304F App version: 6.4.3.
Collabora has its own tracker at https://github.com/CollaboraOnline/online (that repo also contains code for the Android app.) If this is still the case, please repost there.