In reviewing a 2021 tax return for a client we found Sec 179 depr was mistaken entered as prior period depr.  The amount that should have been taken is $7,000.  Can an amended return for 2021 (2022/2023 also) be filed to take the depr or do I file Form 3115 and make correction on the 2024 return?  This is an S-Corp which would mean filing amended for the shareholder also.

Would prefer to file From 3115 and take the depr this year if possible.