What would be the identification reactions of selenate(IV) ion?
You can use reducing agents to reduce the $\ce{SeO3^2-}$ salt to elemental selenium. This paper1 discusses the use of iron(II) salts in acidic medium (phosphoric - hydrochloric acid) as reducing agent. The reaction proceeds at r.t.
You can use other reducing agents like hydrochloric acid, sulfur dioxide, hydroxylamine hydrochloride, hydrazine hydrochloride. The reduced selenium has a red color which turns greyish-warm on warming, but be careful on overheating (boiling or evaporating turns to serious losses of selenium by forming volatile $\ce{SeCl4}$).
References

Rajkumar Kalaparthi , Srija Korapu , Padmarao Chekuri, 2020, New Spectrophotometric Determination of Sodium Selenate [Selenium (IV)] and Sodium Selenite[Selenium(VI)] with Iron(II), and Their Quantitative Analysis of Selenium (IV) – Selenium (VI) Present in A Binary Mixtures, INTERNATIONAL JOURNAL OF ENGINEERING RESEARCH &amp; TECHNOLOGY (IJERT) Volume 09, Issue 05 (May 2020), DOI: 10.17577/IJERTV9IS050094
Vogel, A. I., &amp; Svehla, G. (1996). Vogel's qualitative inorganic analysis