No, one of the conditions of your installment agreement is that the IRS will automatically apply any refund (or overpayment) due to you against taxes you owe. Because your refund isn't applied toward your regular monthly payment, continue making your installment agreement payments as scheduled.

If your refund exceeds your total balance due on all outstanding tax liabilities including accruals, you'll receive a refund of the excess unless you owe certain other past-due amounts, such as state income tax, child support, a student loan, or other federal nontax obligations which are offset against any refund. For more information on these non-IRS refund offsets, you can call the Bureau of the Fiscal Service (BFS) at 800-304-3107 (toll-free).