If the fault is not cleared then the MCB will not reset. Although you some times do get faulty MCB's more likely is the fault is still present.
Light bulbs should have built in fuses but I have found some don't have these I found one from Ikea where there was no internal fuse. So first job is remove all bulbs. In case a light is still switched on. Then try to reset MCB.
If it resets then re-fit bulbs one at a time. I would always use a glove lights should be switched off but mistakes do happen and if there is an internal short in a bulb it can go pop.
If it does not reset then next is look for something else which is powered from lights. For example bathroom fan, Shaver socket, TV booster in loft.
I would not recommend changing a MCB except with old Wilex box where they plug in like a fuse. As inside most consumer units there are live parts even when switched off at the consumer unit.
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