If it’s a wide butterfly you can roll both of the long legs closer to the short strike (keep them equidistant). If the butterfly is slightly in the money this can be done for a credit, which will often be more than the debit you initially paid. This will leave you with a more narrow butterfly completely paid for.
If it’s a losing trade then it’s a losing trade. There won’t be much you can do to save it without adding significantly more risk to the table. Butterflies are made to be low probability trades. They’re inexpensive in nature so the best thing to do is accept the loss and move on to your next trade.