When try to transfer my Overdrive audio book to my older Ipod Iget I must put Ipod in manually manage music

Need help to put my IPOD in manual manage music. When my older Ipod is connected to Itunes it does not give me the option to put in manual manage music mode. I am using a different PC that which I installed my music and audiobooks. My overdrive pgm requires I put it in manual mode to transfer and audio book I have on my PC.