How do you say so be it in Norse?

Norse is not a language in itself. Norse and Nordic are simply Words used to define the area we know as Scandinavia, which, in the modern world comprises several countries, each of which have their own unique languages.

Two examples of rough translation in Norwegian, however

Ikke noe problem (Literally translates as "No problem")

Du trenger ikke bekymre deg (Literally translates as "You don't need to worry")

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Norse is a language, more accurately Old Norse, which is identical to Modern Icelandic.
"So be it" would be translated as: svo vera það

To correct the original Answerer, Norse/Nordic only refer to Norway, and Iceland since it was a colony of Norway.