How do I find a list of all movies or tv shows which premiered before their theatrical release?

No one is going to have an accurate list of ALL such.

At best, someone might have an attempt to list all they can find information on, but there are an insane number of movies and TV shows over all time, and they don’t all have data on all their premiere screenings. And the data there is, is likely not all in one place.

There are probably some sources that make valiant efforts, though probably mostly for the USA, or for Germany (I bet the Swiss might be most likely to have a complete database on Swiss films and TV shows).

I am a little confused by this question, by premiere you mean those private ones they do for critics? I thought every movie with a theatrical release did that because you usually see critics reviews in movie trailers?

Almost every movie made is screened before its theatrical release. As @SergeantQueen said, sometimes it is for critics.

Often it is to test endings and characters – they get feedback from live audiences about what scenes work and what don’t, and in comedies, what is considered funny and which lines fall flat. If you read Mel Brooks’ biography, he describes preview audiences for Blazing Saddles (and other films) which resulted in (sometimes) cuts, sometimes different ending, and sometimes additional footage.

This isn’t new, by the way. In Aljean Harmetz’ book about Casablanca she describes how the ending (this could be the beginning of a beautiful friendship* was changed as a result of audience testing.

But to answer your question: It’s safe to guess that 98% of films are premiered and viewed before thier formal release.

Okay yeah that is what I thought.

I agree with above answer. The ones that do not premire are probably indie films.

@SergeantQueen is correct. Most films get early screenings at film festivals, or for critics, or private audiences.
My favorite was for Brazil. The studio was holding it back, demanding changes.
The full film (minus credits) was screened for Gilliam fans and critics, without telling the studio.
They were surprised when won a critics award.