The pellets are where they can stand to cutback. Feed regular veggies, no treats and cut back on the pellets.
It's important that they are still getting the right nutrients while they are 'dieting'... so a mix of vegetables is important.
Also, ifanyone has a question on what you are feeding and if it is too much or how to cut back- please post it and we can give advice according to their existing diet - butI am not going to recommend starving your rabbit to get weight off.
Also, it's hard to recommend how to help get weight off without first knowing details like what the bunny is currently eating, how much they weigh etc.
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Nadia