You have to be patient, as green peppers take a long time to ripen and need lots of warmth. They will get there soon, probably in September if they were planted fairly early. Even here in France, our outdoor ones are only just changing colour (yellow in our case) and even in the polytunnel we have had just a few ripe ones. But from past experience, we will be inundated with ripe fruit by mid September and October.
(If you really want to 'cheat' you could pick one of the larger green ones and put it in a polythene bag with a ripe banana... in the warm... that would speed it up... but it wouldn't taste as good.)

you can eat them green u know