You will find some recommendations in these discussions:

https://www.researchgate.net/post/Publishing-your-thesis-as-a-book-and-also-publish-journal-articles/1

https://www.researchgate.net/post/How-to-turn-a-dissertation-into-a-book/1

https://www.researchgate.net/post/How_does_a_thesis_convert_into_a_book/1

https://www.researchgate.net/post/Which_is_the_best_publisher_to_publish_the_PhD_thesis/1

https://www.researchgate.net/post/I_want_to_publish_my_thesis_as_a_book_What_authentic_publishing_houses_do_you_recommend/1

https://www.researchgate.net/post/Who_can_provide_information_on_available_free_of_charge_academic_book_publishers_where_I_can_publish_my_dissertation/1

But be warned of predatory publishers like Lambert and others:

https://www.researchgate.net/post/Opinion-required-on-Lambert-Academic-Publication-is-it-okay-to-publish-thesis-through-them/1

https://www.researchgate.net/post/Is_it_worth_publishing_with_Lambert_Academic_publishers/1

https://www.researchgate.net/post/Can_I_trust_to_publish_in_LAP_LAMBERT_Academic_Publishing/1

https://www.researchgate.net/post/Lambert_Academic_publishers_Truth_or_falsehood/1

https://www.researchgate.net/post/Is-LAP-LAMBERT-Academic-Publishing-is-an-authentic-publisher/1

https://www.researchgate.net/post/Is_it_worth_publishing_with_Omniscriptum_Scholars_Press_or_is_it_just_plain_scam/1

https://www.researchgate.net/post/Does_Eliva_Press_legitimate_Is_it_worth_publishing_a_book_with_them/1

https://www.researchgate.net/post/Is_Eliva_Press_SRL_legit_to_publish_your_article_or_research_papers/1