Do not restrict all food. Never starve a rabbit. Their digestion works different to ours or to those of cats od dogs. They need to be able to eat all the time. No intake -> transport in the guts slows down -> that can lead to a build up of gasses, making the issue worse -> that's where real problems start.
They need hay or grass 24/7.
IF there is an actual weight issue, and not a projected one because it's such a huge thing with humans, just fade out too rich stuff. No fruit, except for fingernail sized bits as treats. Same with veggies, they are created for our needs, rabbits can do with a much more meager fare. Depending on which veggies you feed you can reduce or cut out those too, especially if you feed grass or forage anyway.
Reduce pellets too, I use them just as treats to make them go back in their hutches.
Also, give them opportunity to exercise, enough space, a digging box etc.
Most likely they will do fine, the main culprit is us feeding too rich stuff. Don't believe pet food marketing.