What is the requiremint after a person commited one of the major shirks without intention, unknowingly or out of ignorance?
Repent to Allaah, and then feel happy and be hopeful that He has forgiven you and don't repeat it i.e., watch out for unintentional lapses.
Also increase your knowledge of Tawheed and aqidah and of islam in general by reading books. This also may be a means of showing the sincerity of your repentence to Allaah-that you wish to avoid shirk in all its forms and so you are gaining knowledge for that.
if you didn't know that the act you were doing was a shirk , and you didn't know that yet , then god will not count that on you ,and he will forgive as you don't understand that .. and you should ask forgiveness from Allah "the only god of this world" , ask forgiveness and never back to it "the shirk type you were doing" , and also educate yourself more and more of Islam , And the rules in it ..
there is brief instructions on the internet , if you ignore studying the Islam teachings and rules , then god will not excuses you, as its required on Muslims to study what on they and what for they .. there is Do , And Don't .
learn the general rules then get deeper if you found yourself interested in more details .
and remember god raised the responsibility on his nation's faults and forgets.
and god also said : if you weren't making wrongs then god will come up with a new nation that make wrongs then ask forgiveness from him then he absolve for them .
we are not angels that only worship , and we are not animals who eat only ..
we are a middle state , we eat go bath marry , and we worship the Allah .. but that doesn't mean you go insist on the faults or wrongs .
you are required to repent to god in short time and you fall in fault by miss . and the repent is not for they thoe make wrongs and once the death time come they ask forgiveness .