https://www.autodesk.com/products/eagle/blog/route-differential-pairs/The gist is:
1) for every diff pair, name one side abcdefg_P and abcdefg_N.
2) Create a "net class" of, for instance, "USB"
3) In the routing rules for that net class, set "differential, 7mil/5mil" (or whatever your calculated trace/space is)
4) use the "route differential pair" tool (right-click the usual "route" button).
5) Route your pair where you please.
6) At the ends, if you need to, switch to the single-ended tool, and you can finish off the nets individually at whatever trace width you like. This is how you neck down into a connector, join a thinner pad, etc.