Tax law changes

I talked with a Fidelity rep today.  When I asked about using Form W-4R she said that I could use it.  However, five minutes after we ended the conversation she called me back and said that she was wrong.  Form W-4R cannot  be used and Form W-4P must be used.  We then filled out the W-4P form during the phone conversation and I left all lines blank except Step 4(c) (Extra Withholding).  I specified an amount which was a guess of what my tax withholding should be. 

I have two IRA accounts at Fidelity, a 403(B) and a DCP (Defined Contribution Plan).  I have to complete another Form W-4P for the DCP account next week, after the RMD for the 403(B) plan is distributed.  The W-4P for the DCP will be to specify a different amount for Step 4(c).  I then will try to determine if I need to make an estimated tax payment in mid-January, 2024.