How do I enable AirPlay for audio files on iPhone 11 Pro?

I have an

iphone 11 Pro and a pair of hearing aids that are blue-tooth connected to my

iphone. When I open a track on Apple Music or most podcasts the Airplay symbol comes

up on the screen offering me the option of listening “loud” through my iphone’s

speaker or “silent” through my hearing aids. (Opening one of the BBC Sounds “channels”

brings up the Available Devices symbol, which gives access to the Airplay

symbol). So far – so easy!

I also have

some audio tracks which are saved on my iphone as Files (don’t ask why!!). When

I need to listen to one, I open the file, press the “Go” arrow and it plays.

But I have to listen through my iphone’s speaker – the Files app doesn’t offer

me the Airplay or the Available Devices symbol which would enable me to switch the

audio output to my hearing aids.

A solution

would be to have an Airplay or Available Devices symbol always available on my

Home page so that I can switch to my hearing aids when I want to listen to a

File audio track.

Is that

possible and how do I create it?

[Re-Titled by Moderator]