Depends on the form of meditation. For general, workplace-endorsed "mindfulness" meditation, you allow yourself to think whatever you think, but instead of reacting to it, you merely observe and acknowledge that you're having that thought. You don't let yourself get carried along with it though. You let it pass and let another thought come along, observing your own mind. Other types of meditation are about striving to think nothing, and it's expected that you'll fail, and take years to accomplish that after a great deal of practice.

https://www.meditationoasis.com/how-to-meditate/difficulty-meditating

This link also explains some of what I went over with my other comment response to you and a few other things

With meditation you stop resisting any voice in your head and thoughts

They eventually will go away on their own if you don't resist

You do also need to be comfortable, relaxed and in a distraction free environment

Dim your lights and turn off any bright sources of light that keep your body awake

Edit: practicing meditation does also help as well because it does get easier to do over time if you practice