In trans-eQTL SMR analysis, a specified window centered at a trans-eQTL will be tested as a trans-region. trans_chr, trans_leftBound, trans_rightBound are the chromosome, the lower basepair position and the upper basepair position of this region respectively. topSNP is the trans-eQTL which is selected as the instrument.
topSNP_chr is the same as trans_chr but might be different from ProbeChr. And topSNP_bp must be between trans_leftBound and trans_rightBound. Please have a double check with your result file.