You shouldn’t do that. The 737’s autopilot minimum use height is 158ft. This means that you cannot use single channel autopilot below that height.
For dual channel approaches (autoland), we keep the autopilot on during the approach and landing. At 500ft RA we make sure that “flare” mode is armed on the FMA (we say “500ft radio flare armed”). When the main gear touches the runway we’ll disconnect the autopilot and autothrottle and conduct the rollout manually (on fail passive airplanes without rollout mode). On fail operational versions (FlyDubai) you can keep the autopilots on during rollout. You should never disconnect the autopilot on a dual channel approach and continue the approach. If the autopilot fails during an autoland approach, you should go around. The reason for this is that on dual channel approaches, the airplane will trim nose up heavily and you will not have enough elevator authority to push the airplane back on path without trimming heavily, so it’s considered an unstable approach leading to go around.
Single channel approach: Single autopilot usable down to 158ft.
Dual channel approach: Dual autopilot use down to main gear touchdown, provided flare mode is announced as armed at 500ft RA.
For autolands you can use flaps30 or 40. When you do F40 autolands you need to add 140m to your landing distance calculation. For F30 autolands you need to add 185m to your landing distance calculation.