You'll have to take the drive out of the computer. Depending on the machine, you might need a screwdriver. And make sure the machine is turned off and unplugged. Also see if the power supply's I/O Switch is set to Off.
Once the CD Drive, locate the jumper settings on the sticker, and make the white pin go where it should go. One drive should be master, and one should be slave. Doesn't matter which one is.
Your drive won't look like this, but this is an example:
CS is Cable Select.
SL is Slave
MA is Master