OK, I did some reading and all Quicken users are reporting this bug - Quicken does not appear in the Settings App - but according to that forum this can be done from Control Panel - I do wish Microsoft would get some consistency going . . .
Open Control Panel - All Control Panel Items - Default Programs
Click 'Associate file types or protocols with a program'
In the left pane, click .qfx file type
At the top right, choose 'Change Program'
Scroll down and click 'More Apps' - does Quicken Appear
If not, scroll down and click 'Look for another App on this PC'
Then Navigate and find Quicken.exe and set the file association
Do the same for qif files
Hopefully that will sort this out for you . . .