Ghusal e janaba was mandatory but i forgot and did normal ghusal and did faraiz of Wudu at end. Then recalled in office that i had to do ghusal e janab. So guide how to handle such situations and how about praying salah in that situations. Since can not rebath in office.
If you mean you forgot that you were in the state of major ritual impurity and you just took a normal shower to clean and freshen up, all the prayers you had prayed were invalid and you must perform a new ghusul with proper intention and redo these prayers.