Linear cryptanalysis complete key guessing In linear crypt analysis, partial sub keys are guessed and verified for its correctness with the help of plaintext and ciphertext.

From the partial sub key, how it is possible to guess the complete key?

For example, if we are guessing and verifying the key bits $K_5,K_6,\ldots,K_8,K_{13},\ldots,K_{16}$ for its correctness. But how can we get the complete key? That is $K_0, \ldots, K_{16}$.
As in @Guut Boy's answer it may be possible to brute force the remainder of the key bits. 

Another technique would be to find  another multi round linear characteristic which can be used to brute force another subset of key bits. Of course your success probability in doing this would depend on the overall probability of the new linear characteristic, but if the key bits determined by the new characteristic overlap some of the key bits already guessed, this may speed up your attack.