Upd

commands.py

@@ -271,9 +271,9 @@ async def bday_handler(bot, event, command):
     try:
       entity = await bot.get_entity(user_id)
     except ValueError:
-      birthdays_list += 'Ошибка!\n'
+      await bot.get_participants(await event.get_chat())
 
-      continue
+      entity = await bot.get_entity(user_id)
 
     birthdays_list += get_user_name(entity)
     birthdays_list += ' — '