What should I do regarding the 1000 Saudi Riyals I took from the fictitious insurance claim, knowing that I have repented, that I have no contact with the person who took the rest of the money, and that the third person involved took nothing?

What you have done is unlawful, as it involves taking others' money through deceit and forgery. All of you must repent to Allah. You, as the one responsible for the money from the insurance company, must return it to the entity from which it was taken, if possible. Otherwise, spend it on the general welfare of Muslims or give it in charity to the poor, after deducting the insurance premium you paid. You should then seek reimbursement from the person who denied their responsibility for what you paid to them.