Use a stapler.  Paper clips come loose.

If you're asking where to input the tax withholding, it's on Page 3, Schedule G, Line 16:

Line 16—Credit for Tax Paid on Undistributed
Capital Gains
Attach Copy B of Form 2439, Notice to Shareholder of
Undistributed Long-Term Capital Gains.

Or is this a "how to e-file" question?  Same way you attach images of other documents.