I've never heard that missionaries played a significant part in the African part of the Atlantic Slave trade. I could be wrong about that, but my understanding is that the people running the slave trade, both the European slavers and their African collegues, weren't interested in that kind of stuff, and that it was in the later extension of imperialism and colonialism that the role of missionaries became important.

There are two aspects to "apologies". One is that they are a way of making people today aware of some apalling things that have happened in the past of our civilisation, and of the continuing consequences of those things in the present.

And the other is that they are a way for society to accept responsibility to repair the evil consequences of that past history, insofar as it can be done, and to make use of the resources available largely as a direct result of slavery to do that.