How to tenderize bell pepper skin / peel
You can't. If you want a pepper puree, you have to remove the skins mechanically. Else you get a puree with "scales" of skin inside. 

You also mention making a stew out of the peppers. The skins are normally not removed for a stew, just eaten along. Many people prefer to not add the pepper at the beginning, but only to throw it in for the last 15 minutes, so it doesn't overcook. This results in pepper pieces which are crisper overall, so it might not be to your taste. 

If you absolutely need a stew in which the pepper is soft but there are no skins, you can probably char the pepper and peel it first, then cut up the peeled pepper and use it in the stew. But if you put it in as early as the meat, it will probably disintegrate and not be recognizable as pieces any more. If that's your goal, you can save a lot of work by mixing into your liquid ready made ljutenica (which has more vegetables and a more complex flavor profile) or pure bell pepper paste, if you can get it.