I think that you will find that the very concept of "meaning of life" is meaningless. There is no concrete, real-world thing that it refers to. However, some people do attain a certain bodily and mental state where they feel they are missing something, they feel like life is incomplete. This sometimes manifests itself as a nihilistic worldview (among other effects). It is also almost always accompanied by a feeling of disconnection from others, from society.

Now, for someone who is not in this particular bodily (and mental) state, life itself is a joy. The concept of meaning of life doesn't even come into question, because if you love waking up in the morning, love the work you're doing, the people you interact with and society and the world itself, you don't feel like you're lacking anything. There is no need for further meaning.

Also, this state, like all other bodily functions, is not a discrete, binary switch, but a continuous biological mechanism that takes a spectrum of values. It can be measured by simple tools such as the activation of the vagus nerve, brain activation pattern revealed on an EEG and so forth.

As for how to change this bodily function, unfortunately that is still a bit of a mystery. Some find that seeing a therapist helps, changing of your personal circumstances often helps as well. There are other promising mechanisms such as neurofeedback, but none of them have a perfect track record.