the theory behind it is that a lot of behaviour is actually attention seeking behaviour. That the child deep down isn't feeling loved and secure, and so they kick off, kick against boundaries etc. Love bombing is giving them focused positive attention, letting them know they are loved and so making them feel secure, loved etc, and therefore decreasing the bad behaiour.
There is also the idea that you have a sort of love bank. When your love bank is full, you feel good, confident, loved, secure, happy. When your love bank is empty you feel the opposite of all that. Love bombing is about filling the bank up again.
Practically, you love bomb a kid by taking some time out of normal stuff. You let child set the agenda, go with what they want, lots of focused attention, lots of 1:1 time, and letting them know they are important, valued and loved. It can be a whole day. It can be a shorter time, it can be repeated as often as you need to.