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If it's a diff pair then you want to have control over it yourself and route it where you need it to go, away from areas that you do not want it to go to etc. Then you will want to length match it.
All this is best done as a manual task, as Marce says - use trunk routing (select both start pads then manual route) and route as a pair to the end pads and (RMB - automatic reconnect on).
If you need to be doing some length matching then you may need to RMB & decompose the trunk so that you can do that.