In Android you'd usually go to settings/app settings (which on a Boyue means, finding the standard android settings first (its burried under about device (the top most arrow (right) in the UserSettings app, besides the image of the device))), then select the app thats currently opening your .cbr files as a default, and looking for the 'open by default' option and then select clear defaults.
The next time you open a .cbr from a filebrowser, Android should give you an option to open it with any app that supports .cbr, and you can set it as a default from there.
Before you do that, try downloading another filebrowser like "Total Commander", and try starting a .cbr file from there first. Maybe its just Boyues default file browser that defaults to the Boyues reader app by default. (Which, if so, might not be changeable).
But in general, on Android, thats how you do it.
(Havent done it myself, so report back if it works.
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