Need to restore data from iphone5 to iphone3gs

Hello - please advise me. I have contacts and other data on my iphone5 - and need this data on my old iphone3gs. I have made a backup of my iPhone 5 (IOS 8.3) on my mac - but the 3gs cannot see that backup so am unable to restore to the iPhone 3gs (IOS 6.1.6). Every time I connect my 3GS to my Mac iTunes only allows me to backup - not restore. I don't want a backup of the 3GS.

Would appreciate any help.

thanks

(iMac 2011 Yosemite)