The time to do this was through a direct division of retirement plan assets at the time of your divorce. Have you already taken a check for this money? Or is it still sitting in your spouse’s retirement plan???
If it’s still in your spouses’s plan, then you can present the plan custodian with a QDRO order (qualified domestic relations order) and they will ROLL IT OVER DIRECTLY TO A NEW CUSTODIAN, as an IRA rollover in your name. But first you will have to open the account at the new custodian (I suggest calling Fidelity — 1-800-FIDELITY) where they will set up the account. They should handle this entirely with your spouse’s plan — and each plan will need a separate, notarized letter of instructions, including the court order.
If you have already taken the distribution from your spouse’s plan it may be too late to do a rollover. But in any case, you cannot roll it over into a 40l(k) plan. And you should start your own, separate IRA to start saving for the future based on your own work income.