If its very convex, then spot work the middle out, or you will just be copying the profile with a flat lap, no matter how meticulous and careful one is.
More of an issue with a no.5 and longer.
Best just clean the sole if you don't have a good straight edge for reference,
Id be more concerned about the iron lapped and cap iron fitting than working the rest to an extremely high standard.
If you want to smooth with it, then follow David's advice (youtube David W)
about the most through instruction you will find, plenty of bad advice out there by some of the most popular gurus.
(if you don't want to scrape flat work that is, why ever one would want to)
A long reach angle poise or handy lamp with a good large shade 7.1/2" will give sufficient light, the shade on a normal wee bedside lamp is not good enough.
A hone whatever you like, and a bench or something suitable to plane on is what you need,
Can't do much without those things, and it's a frequent occurrence for many to blame the tool and go fiddling with it, when the problem turns out to be the B&D workmate they're working on.
Just saying don't go mad lapping anything but the iron, until you at least have a suitable thing to plane on, be it a big sleeper or a countertop against a wall,
It needs to be rigid enough or able to be shimmed flat if you want to have an easy life learning how to use a hand plane.
No need for vices or anything, just something that also butts against the wall
to act as a stop, clamped down batton if preferred.
All the best
Tom