401K contributions made from your paycheck (unless Roth 401K) are already not included in your income.
If you took out the max ($100k) in 2020 as a disaster distribution, and were going to split it up over 3 years, then your taxable income on the distribution would be $33,333.33 each year. For 2021, the max 401K contribution (under 50) is $19,500 and max IRA is $6,000. If you wanted to repay the $33,333.33, you would have to classify the repayment separately as a rollover contribution so it doesn't count towards your max 401K or IRA contribution limit for 2021.
If you didn't make any of these rollover contributions to repay your disaster distribution, then you would just pay taxes on the 1/3 of the distribution you took in 2020 each year for three years.
BTW, I'm not a lawyer and this is not tax advice, just personal experience. I had to classify each of my repayments as a rollover contribution otherwise I would hit the max and the 401K/IRA administrator wouldn't allow it.
