To combine both halves of Webb, engineers carefully lifted the Webb telescope (which includes the mirrors and science instruments) above the already-combined sunshield and spacecraft using a crane. Team members slowly guided the telescope into place, ensuring that all primary points of contact were perfectly aligned and seated properly. The observatory has been mechanically connected; next steps will be to electrically connect the halves, and then test the electrical connections.
Source:
https://phys.org/news/2019-08-james-webb-space-telescope.html