What percentage of 401k and/or sep accounts has to be withdrawn starting at age 70 1/2. How does the percentage change every year.
Note: I am not asking for a dollar amont, I want to know the percentage.

That is entirely dependent on which plan administrator you have as it varies from plan to plan. Contact your plan administrator.

Its not quite that simple. The Required Minimum Distribution is based on anticipated life expectancy. Not plan administrator.

There are a number of RMD calculators on the WEB. Here's one: Required Minimum Distribution Calculator – FINRA

The IRS determines the required minimum distribution, not the plan administrator. The initial distribution must be made by April 15 of the calendar year following when you turn age 70-1/2, and by December 31 of subsequent years. Here's the IRS table - you divide your December 31 account balance by the expected "distribution period" (esssentially your life expectancy):

www.irs.gov/pub/irs-tege/uniform_rmd_wksht.pdf

The resulting percentages turn out as follows for the first five years:

Age, RMD %
70, 3.65%
71, 3.77%
72, 3.91%
73, 4.05%
74, 4.20%
75, 4.27%
etc.