Are you asking for a "delete all spam comments" button within ASB? That should be easy to do. Or do you want to have a "delete all spam comments with spam reason X" filter?

We do have the "Delete comments by spam reasons" option. And we have the "Delete existing spam x days" option. Having a combination of both would be nice (so not delete comments with "any" reason after x days, but only those with a specific reason).

Are you asking for a "delete all spam comments" button within ASB?

No.

Or do you want to have a "delete all spam comments with spam reason X" filter?

No. These are pending comments. So I would like to re-analyze them. And maybe some sort of "This is spam, please mark every comment with the same content/author/IP as spam too"-button, or something else which is preserving valid comments which could be in this huge amount of pending comments. There is no spam reason for pending comments, so this is not what I want.

We do have the "Delete comments by spam reasons" option. And we have the "Delete existing spam x days" option. Having a combination of both would be nice (so not delete comments with "any" reason after x days, but only those with a specific reason).

This does not help for those pending comments. This would help for new comments only.

Ah, now I get it. That would really be a very key functionality, especially if you install the plugin after you've already received lots of spam.

That would be a cool feature.
If its okay, I would label it in some 3.x milestone?

20k seems to be a "normal" spam wave ...

I just looked at the comments list screen and thought about where to put those actions. In the first step, I would begin with the action to re-analyse all pending comments. I thought about putting that as a button in the AB settings screen, because in most cases, that would be a one-time action, nothing that the user needs often.

What do you think?

Not sure. The edit-comments.php page is very full. Not easy to add a new button. Although this is the first page I would look at if I have comment spam and not the setting page of ASB.

@Zodiac1978 this feature is when you did not have ASB installed and you install it after you have 20k spam comments.
So it makes sense to be in settings:
You detect the spam, install the plugin, configure the settings and then from the same page, run it for current pending comments button.
Job done! :)

PS: I just installed this plugin on a project for those reasons, and I will use WP CLI to remove all comments on pending, probably losing some real comments in the process. I won´t even go into the edit-comments page at all.