No, you are not able to amend the tax returns to elect to make these contributions non-deductible, because the time limit for filing an amended 1040 (1040-X) has passed.  Per the IRS, "Generally, after you file your return, you can change a nondeductible contribution to a traditional IRA to a deductible contribution or vice versa if you make the change within the time limit for filing Form 1040-X." The time limit is 3 years after the date you filed your original return or within 2 years after the date you paid the tax, whichever is later.

It is possible to initiate a Roth conversion, where you would pay tax now on both the contributions and earnings, and then the future earnings would be tax free. To read more about Roth conversions, see: Converting IRA to Roth IRA

@uocan [Edited 01/21/24 2:12 PM PST]