The materials given by Kaj Chieh Shih (Lin's grammar and itaigi.tw) are very good. There are more (including links to free video training classes and apps) over here: https://mikusworld.wordpress.com/category/language-resources/ (look under "Hokkien" at the top). The first class in the youtube video series has a good explanation of the different tones and tone changes.

In terms of people - there used to be several community tutors here on italki who teach Taiwanese (Taigí) and can be found through the teacher search. Let me know if you cannot find any, I know at least one ;-).

我用過最好的臺語文法書是:

https://www.amazon.com/Taiwanese-Grammar-Reference-Philip-Lin/dp/0996398201

發音:

https://itaigi.tw/

(輸入漢字後即可聆聽。)

Ekaterina你好，台語真趣味，袂困難--啦，請你先莫按呢想，你就會學較緊！

Ekaterina lí hó，Tâi-gí tsin tshù-bī, bē khùn-lân--lah,tshiánn lí sing mài án-ne siūnn, lí tō ē o̍h khah kín！

寬寬仔來，咱會使做伙練習~

Khuann-khuann-á  lâi, lán ē-sái tsò-hué liān-si̍p！

Hello Ekaterina, Taiwanese is very interesting, not diffcult . Please don't think like that, and you will learn it quickly!

Take it easy, we can practice together ^^