If your e-filed tax return is rejected by the IRS then you can make your corrections and re-file. If the tax return is Accepted by the IRS, then you need to wait for the tax refund to be received or the taxes owed and paid to be processed before attempting to amend the filed tax return.
Use this TurboTax website to check the status of an e-filed return and if it was either accepted or rejected - https://turbotax.intuit.com/tax-tools/efile-status-lookup/
See this TurboTax support FAQ for amending a 2018 tax return originally completed and filed using the online editions - https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-turbotax-online-return/00/27577
