This usually happens because the robot is trying to clean an area it can physically fit into, but then can't find its way back out. There's a specific setting in the app for this.
First, use the iRobot HOME App to set up Keep Out Zones. Draw a virtual boundary around the area under the couch to tell the robot to avoid it entirely. If you don't have the app connected, you can use the included Dual Mode Virtual Wall barrier. Set the switch to Halo mode and place it near the couch leg. This creates a circular invisible barrier about 12 inches across that will stop the robot from entering that zone.
If that didn't work: The other possibility is that the robot's front caster wheel is jammed with hair or debris, which affects its steering and ability to back out. Pull firmly on the front wheel module to remove it, then pull the wheel out of its housing. Clear any wrapped hair from the axle and inside the cavity. Make sure it clicks back in place and spins freely.
Heads up: A clogged front wheel that isn't spinning freely can actually damage your floor over time. If cleaning it doesn't fix the steering, you should contact iRobot Customer Care.