  Iron chalcogenide Fe(Te,Se) attracted much attention due to its simple
structure, which is favorable for probing the superconducting mechanism. Its
less toxic nature compared with iron arsenides is also advantageous for
applications of iron-based superconductors. By intercalating spacer layers,
superconducting transition temperature has been raised over 40 K. On the other
hand, the presence of excess Fe is almost unavoidable in Fe(Te,Se) single
crystals, which hinders the appearance of bulk superconductivity and causes
strong controversies over its fundamental properties. Here we report a
systematical study of O$_2$-annealing dynamics in Fe$_{1+y}$Te$_{1-x}$Se$_{x}$
by controlling the amount of O$_2$, annealing temperature, and time. Bulk
superconductivity can be gradually induced by increasing the amount of O$_2$
and annealing time at suitable temperatures. The optimally annealed crystals
can be easily obtained by annealing with ~ 1.5% molar ratio of oxygen at 400
$^{\circ}$C for more than 1 hour. Superconductivity was witnessed to evolve
mainly from the edge of the crystal to the central part. After the optimal
annealing, the complete removal of excess Fe was demonstrated via STM
measurements. Some fundamental properties were recharacterized and compared
with those of as-grown crystals to discuss the influence of excess Fe.
