You can easily brute force the word using https://btcrecover.readthedocs.io/en/latest/

These are all the BIP39 word, they are just 2048 in total:

https://github.com/bitcoin/bips/blob/master/bip-0039/english.txt

The reason I give you the word list is if you have some letters that start the sixth word, the better to choose form the suggested letters as few letters will be left. But if you are not able to recover it easily as you do not know any letter that the word starts from at all, then use Btcrecover.