Paying tax on Required Minimum Distribution? E.g. distribution is $10,000 and I've paid tax on $12,000 w/ 8606. Can I choose to not pay tax by using part of the $12,000?

How to pay tax on Required Minimum Distribution, exactly? E.g. distribution is $10,000 and I've paid tax on $12,000 using form 8606 over the years.  I've read all the RMD Q&A but do not see a clear-cut answer to this example. Can I choose to not pay tax using part of the said $12,000?  If not, what is the formula to pay tax?