Since you mentioned FL Studio in another thread, I assume you have FL?
In FL, you can use the Fruity Love Philter, set it to default and turn off the filters, and go to the LFO section and turn on pan LFO - autopan. This would be the most simple way OTB with FL plugins I think.
If you want a more specific pan pattern like BC described, you can instead use the envelope-section for the pan on the Love Philter, make a custom envelope, and set it to loop.
Or you can actually set an automation clip to act as an LFO, so you can just add an automation to a pan knob. Though I see no need to make it that way, but technically you can.