T = readtable('my_excel.xlsx') ;
[val,idx] = min(T.(2)) ; % get minimum from col2
iwant = T.(1)(idx) ; % get the value
If you proceed with xlsread which is outdated:
[num, txt, raw] = xlsread('my_excel.xlsx') ;
[val,idx] = min(num(:,2));
iwant = num(idx,1)