Hi,
What I've done in a similar situation is:
1- Create the new destination collection in the corresponding community.
2- Export the metadata of the items from the source collection that I want to move.
3- (This isn't necessary, but I'm very conservative about it.) I delete all columns from that CSV file except for the ID and collection columns.
4- I use one or two of those items as a test, and delete the rest of the rows.
5- In those test rows (records), I change the collection number to the new collection in the corresponding column.
6- If I'm satisfied with the result, I continue with the remaining items.
7- I delete the original collection, which should now be empty.
This is just one method I'm sharing with you. I'm not sure it's the best, but it's what I've used. I hope it helps.
Best regards,
Jorge