I bought a new energy-efficient furnace and A/C in 2022. Am I eligible for that tax credit still? I have already submitted and received my 2023 return.

You can claim the credit by amending your 2022 tax return.  For tax year 2022 the credit would be $300.

See this TurboTax support FAQ for amending a tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-already-filed/L4VjJ9BA2_US_en_US