Well, you've already had them together now, so it won't help this time, but next time, PLEASE keep new birds separated from your flock for a full month. You could be bringing in a disease that will kill your whole flock!! It is NOT worth the risk!! Biosecurity is a real issue that we all must follow in order to keep our birds safe.
Now, as to the roo. I'd put him in time out! A dog cage, bird cage, rabbit cage, whatever I had available to use. Since you're getting rid of him anyway, there's no need to work on his attitude problem.
I'm adding a link that I do hope you'll read and watch this BYC members heartache from adding a pair of new silkies.
https://www.backyardchickens.com/forum/viewtopic.php?id=196261
And yet another that had to cull her entire flock as well.
https://www.backyardchickens.com/forum/viewtopic.php?id=181490
Now, as to the roo. I'd put him in time out! A dog cage, bird cage, rabbit cage, whatever I had available to use. Since you're getting rid of him anyway, there's no need to work on his attitude problem.
I'm adding a link that I do hope you'll read and watch this BYC members heartache from adding a pair of new silkies.
https://www.backyardchickens.com/forum/viewtopic.php?id=196261
And yet another that had to cull her entire flock as well.
https://www.backyardchickens.com/forum/viewtopic.php?id=181490