1、make sure your iphone is the latest one .if it isn’t ,then get it updated to take advantage of the latest features.
2、open iTunes on the secondary computer and connect your iphone with it .choose cancel, when a widown pops up asking for erasing and rewriting of data.
3、select “Manually Manage Music and Movies” option under the summary tab ,transfer music from that computer’s iTunes library to your iphone .
Once you have purchased apps, they stay purchased and you can reinstall any apps from an authorized PC, after signing in to your iTunes account. So that's how you can sync iPhone with two computers and protect your data from getting erased!
If above can’t help you , here I share a page for you “how to transfer music from iphone computer“ Maybe this is useful for you
<Links Removed> Possible malware hosted at recommended download site hotdownloads.com.