أعوذ بالله من الشيطان الرجيم

بِسْمِ ٱللَّٰهِ ٱلرَّحْمَٰنِ ٱلرَّحِيمِ

As Salaamu Alaikum Wa Rahmatullahi Wa Barakatuh,

Based on your specific question and information provided.

From the Jurisprudence Perspective: 

You should perform the Tashahhud in the same as explained in the book of Islamic Laws (Resalah) of your Islamic Scholar (A Qualified learned Scholar of Islam / Jurist / Mujtahid / Marja ).

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Principles / Fundamental / Roots of Faith ( Usul al-Din). Ash hadu anna Amiral Muminina’Aliyyan Waliyyullah (i.e. I testify that the Commander of the Faithful Imam Ali (Peace be on him) is the vicegerent of Allah). Imamat / Waliya / The Divine Leadership is part of our Principles / Fundamental / Roots of Faith ( Usul al-Din). It is necessary for a Muslim to believe in the fundamentals of faith( Usul al-Din) on the basis of proof and he cannot follow anyone in this respect . (Taqlid is Haram ( Forbidden) in Usul al- Din).

Branches of Faith ( Furu al-Din). Regarding the Salah. It is part of Branches of Faith ( Furu al-Din). In Islamic Acts we have to be either a learned person in Islamic sciences, a person who can understand what needs to be done in Islamic acts, or follow a learned person or act with precaution ( ihtiyat ). 

Kindly, review the following Q & A for related topics for overall understanding of these issues.

https://www.al-khoei.org/Questions/tashahhud/

https://www.al-khoei.org/Questions/why-do-shias-mention-imam-ali-in-their-azaan/

والله العالم‎
(and Allah(awj) Knows best)
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