You cannot.   All joint income must go on a joint tax return.  A sole proprietorship LCC goes on the 1040 Schedule C.     If the joint return was filed without it then it must be amended to add that income.

Is it a Single Member LLC?  Is it an S corp?  If you want to file it separate you will need to file separate 1040 tax returns as Married filing Separate and not a Joint return.  But MFS is the worse way to file and has the highest tax rates.  And you can lose several credits by filing Separate.  

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@VolvoGirl wrote:

Is it a Single Member LLC?  Is it an S corp?  If you want to file it separate you will need to file separate 1040 tax returns as Married filing Separate and not a Joint return.  But MFS is the worse way to file and has the highest tax rates.  And you can lose several credits by filing Separate.  

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At this point that is not simple.    Your spouse must amend and change the first taxpayer on the joint return to filing separate, then remove the second taxpayers (spouse) information.    Then you file a new separate return.  All of those will need to be mailed since amended returns take 4-6 months to process.   Also, tax law does not permit changing from joint to separate after the due date of the return which is May 17 this year.

If you live in a community property state then you must allocate income between spouses and doing that with a LLC  involved might require professional help.

Overall you will both probably end up paying much more tax filing separate.