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Hi Prabin,

>>>>>I can not add license to the autocard2020 trial version
What steps have you taken to do this?

Have you tried steps described here:
https://knowledge.autodesk.com/customer-service/download-install/activate/convert-trial-to-subscript...
you have to perform steps from "Update License" section.
On Mac Manage Licence button is on "About AutoCAD" window - menu AutoCAD -> About AutoCAD.

You may also try to ask your question on dedicated Forum:
https://forums.autodesk.com/t5/installation-licensing/bd-p/24