If you’ve got routes near you with hill climbs, just ride them a lot.
Weight obviously is an issue, but for climbing legs just need to get fitter, but you need to regularly exercise them. I find just a couple of weeks without riding and big climbs can be a struggle. Regular riding will hopefully help with the weight also of course, though careful not to pig out on big meals after a big calorie burn 😀 (which is my problem, though at least I don’t put on weight, but I would if I stopped riding).
But, take your time, push bits, rest, don’t overdo it first time. Have fun, go back and see if you’ve improved 😀