The most sensible place to start looking for a manual for your Bernina Bernette 334DS is Bernina themselves, and their homepage even has a section for out-of-date manuals at bernina.com/en-US/Support-5.
If Bernina can't help you, plenty of other places online can: Try manualsonline.com/support/bernina, where a forum user has posted a link to a downloadable copy of the Bernette 334DS manual.
Having problems with that site? Then give pages.sewing-machine-manuals.com a try, although bear in mind this site charges for downloads, and for sending copies through the mail.
Away from specialist sites dealing solely with manuals, you could turn to the online sewing community forums. These include sewusa.com and sewing.patternreview.com, where you can post a question asking for help, and a fellow Bernina user may be able to assist.
For answers to similar Blurtit questions, take a look at Where Can I Find A Manual For My Bernina Serger 1100DA? or Need Manual For A Bernina Bernette H70?