hello ahsaan,
go to transient solver >> and tick store results data in cache.
once simulation is over goto the simulation folder (should be same name as your CST file name) >> Result >> Cache >>and then you can see different folders with RUN 00XX.
U should use MACRO - WIZARD - COMPARE MULTIPLE RUNS,
but be sure - as the other user posted - that you have stored
before all runs in cache, this is an option of the solver dialog
box.