the IRS may have taken your refund to lower the amount owed for those other years. if so it should be reflected in your account balance. if you go to the IRS website and check the status of your account you would see the balance due for those year(s) reduced. if you owe state taxes, child support or there are other offsets your refund could have been seized. in any case, if your refund was taken you should have gotten a notice. have you use the TT tool or IRS website to check your refund status? if not, do so before proceeding. because of the pandemic, the IRS is behind in issuing refunds. so it may just be a matter of having to wait.
Even if you are on a payment plan any and all future refunds will be taken to pay down the balance due ... if you read the installment plan agreement it tells you this will happen. When you actually pay off the debt then any excess refund will be sent to you. Watch for a notice in the mail explaining the situation.