Can I change the subtitles size within Apple TV app?

I'm using the Apple TV app on the iPhone and on the Fire TV stick and I am having an issue with surtitles size.

I can switch the subtitles ON, however size of subtitles is too small! Especially on the TV.

Where is a setting to change the font size in the Apple TV app? I searched on the web, but I can not find any instructions talking about changing subtitles font font size within the app.

I have a good sight but default size is really small. Older people and people with impaired vision probably can't read those default subtitles at all!