leave (someone) to it
To allow someone to do something without one's involvement or interference; to withdraw from someone so they can do or finish something alone. I just had a question about the order, but I can see that you're busy, so I'll just leave you to it. We left him to it after he made it clear that he didn't need our help.
leave someone to it
to withdraw and allow someone to finish something alone. I hate to leave before the job is finished, but I'll have to leave you to it. I will leave them to it. I have to go home now.