How to apply Safe Harbor Method

How to apply Safe Harbor Method ( Simplified Method ) to respond IRS letter to submit 4626 form? Or, can I just amend by 1120-X to click " Yes" on Schedule K Line 29 without applying Simplified Method?

If I want to respond IRS by Form 4626, it looks like I only can fill in Part I, and some blanks on Part II, because my C corp is neither consolidated , group, or more than 500 million corp.

Please advise, need help!

Thanks

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