This question already has an answer here:
Is there a way I can search (not just see after finding flights) for flights that use a particular maker's aircraft, say if I want to avoid or have a particular affinity to one of the major makers?
This question is similar but ended up (3 years ago) with a suggestion on viewing the aircraft types after completing a search, which makes it quite tedious.
It should be possible to make a list of airlines and use checkboxes on the search page to include only appropriate companies- but many companies (as just a couple of examples, Cathay Pacific and Hainan Airlines) run a mixed fleet directly or through their subsidiary connector airlines, complicating things, without even getting into codeshares.
Edit: Nate has pointed out a similar question with an answer that works for this situation.