Gazebo move a model's child link to a certain position in the world

Hello friends,

– I’d currently doing one project, I need attach Model A’s one child link a to Model B’s child link b, I can use one plugin to do the attach, but I hope these two links are attached each other, there should no space in between, only using joint->Attach(link1, link2) will keep the initial distance between these two links, are there any ways I can first move the link a close enough to link b then I do the attach ?

Thanks in advance !