\documentclass[a4paper,12pt]{book}


\usepackage{amsmath}


\usepackage{xepersian}



\settextfont[Scale=1]{Yas}
\setlatintextfont[Scale=1]{Yas}
\PersianMathsDigits

\begin{document}
$$ \sideset{_{LowerLeft}^{UpperLeft}}{_{LowerRight}^{UpperRight}}\sum_{B}^{T}$$
\end{document}