Does committing sins after Umrah invalidate its reward, and what should I do to return to the state of faith I was in after Umrah?

You must give up sins and repent sincerely, resolve not to return to them, and increase good deeds, for repentance erases what came before it, and the one who repents from sin is like one who has no sin. Falling into sins does not affect the validity of 'Umrah or other good deeds; rather, it is acts of disbelief in Allah that invalidate them.