I need to change my W4 withholding for my Arkansas teacher retirement pension income. I need to get a specific amount withheld. Can you tell me what to do?

On line 4 of you Arkasas W4, you will enter the additional amount you want withheld.  

Then you will take the $350 per month multiplied by 12 months for the yearly amount and then divide the yearly amount by the number of pay periods you have.  It will be 26 if you get paid biweekly and 52 if you get paid weekly.  Then enter this amount on line 4 of the W4.