That isn't a backflow preventer (aka "check valve") it is a union. Only way to fix that is to replace the piece on the right which means cutting back the plumbing until you have enough room to add a patch piece. This also assumes you can find the same model union as they are usually proprietary. But that looks like the usual union sold at Home Depot.
Yes as long as it is the same one. But that does look like the standard Home Depot model. Not really a huge deal since it looks like you have a threaded fitting to the left side that you could replace up to the threads if needed.
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