2nd Apple ID with many book purchases

I have 2 Apple ID accounts. I purchased lots of iBooks& audio books on the 2nd account, but can’t access bc I no longer have a second work phone. How can I use my purchases on my current device? Can I merge the two accounts? I still have access to the acct, but it says if I download, i won’t be able to make other purchases for 90 days? I don’t want to mess up my primary account.