SDK Manager offline installation guide

Dear All, My desktop operating system uses Ubuntu 18.10 already. When I try to run SDK Manager to install JetPack to AGX Xavier, it can not continue, because it need Ubuntu 18.04. Can I use a 32 GB SDCARD with Jetson Nano image and put it into AGX Xavier slot to boot it up and try to install JetPack 4.2 from inside? Please help to overcome this problem. Thank you very much in advance. Warmest Regards, Suryadi