You will be able to mail out the form 8915-E with your amended return. The form 8915-E will be generated on your amended return if you indicate that you will spread your tax payment over the three years allowed.
Since you withdrew money form a traditional IRA account and then put it into a ROTH IRA, that will not qualify as an allowable recontribution. This is not explicitly stated in IRS notice 2020-50, but I assume this is so since you have to pay tax on the traditional IRA distribution as you would have to have done if you did a ROTH IRA conversion. So, there would be no tax advantage to recontributing the funds.
The 401-K contributions aren't going to work as a recontribution, since they will be reflected on your 2021 tax return as a reduction in your wages as reported on your W-2 form. As such, they will reduce your tax income in 2021, but to report the recontribution, you would need to report it on your 2020 tax return, so there would be a duplication in reporting. However, you may want to talk with your employer to see if there is anyway they could not report the 401-k contributions on your 2021 wages, but I don't think that is possible.
You can read more about this in IRS notice 2020-50 here IRS notice 2020-50.
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