If you don;t feel up to poking holes and lacing just yet you can often get 90% of the way there with a simple re-blocking. I've successfully re-shaped a few over the years in worse shape than that, ultimately it doesn't always hold, or at least not for as long as lacing but it's an easy first option.
The trick is to let all the tension off, then soak it for a while until it's nicely compliant but not floppy. Then, depending on how out of shape it is you either need to stuff the underside with something to re-shape, hard modelling foam works, or at a push rags and wood. Then you need something wrapped around it to pull the sides in, I've used an old tea-towel (to protect) and then cinched a few toe-clip straps around that to pull it all back into shape. Then you need to find a flat surface to lay it upside down on, and then some hefty weight on top of it and leave it to dry out.
If this all goes according to plan then you should end up with a nicely re-shaped Brooks. In some cases when they are particularly badly out of shape it can take a couple of attempts, one to get it roughly in shape, and then another with better blocking and/or strapping to get it finished off.
Once it's back in shape time to get the leather treatment on it and gently bring it back up to previous tension, then maybe a smidge more, but certainly don;t tension while wet!
