How to make a guitar sound like a bass? Unplug the guitar and plug in a bass instead. Fastest and easiest way to do it.
Can't afford a bass you say? Take all the time you would waste trying and failing to get your guitar to sound like a bass, and instead use that time and effort to work a shitty job for a couple of days and buy a cheap bass on ebay.
Or you could borrow one from a bass playing friend, maybe get him to put down the bass tracks for you? You could even start this really cool thing called a band!
It's something people used to do before everyone started making music on their own in a bedroom, posting questions here about how to make programmed drums sound real, how to make amp sims sound like real amps and how to make a guitar sound like a bass.