While we don't have a transfer ownership option, below is a 'hack' to adding presentations between accounts.
You will want to begin in the account with the presentations that you want to relocate. This is referred to as Account 1 below. Account 2 is the account you want to add/relocate the presentations too.
Step 1: Add Account 2 as a collaborator to the presentations in Account 1.
Step 2: Log into Account 2 and duplicate the shared/collaborated presentation(s) from Account 1 into your library. Shared presentations have the icon at the top left corner. You will have to click the drop-down arrow at the bottom right corner of the shared presentation then click Duplicate. This will copy the presentation into the new library and that copy will not be connected to your other account.
Step 3: Go to the original shared presentation and remove it from your library.