I believe FIFO is the default, not an election.

Thanks! Will you know how do I select another methods i.e. 'Specific Identification Method' that is listed in Pub 538? I believe IRS allows weighted average method as well

No. I haven't had a new business with inventory in years.

ProConnect has a neat FIND THE INPUT feature. For your question: Check Return > Look at the 1125-A > Line 9 a (iii) has a check box > Click that box.

This feature works for any line or box that is highlighted in blue.

To determine the value of beginning and ending inventory we need two things - a method for identifying the items in your inventory and a method for valuing these items. I believe the original intent of section 9a was to specify the method for valuing the inventory i.e. LCM, Cost , Retail etc.. Are you sure the others option in 9a can be used to specify cost flow methods like specific identification, weighted average?

"how do I select another methods"

Have you read the instructions here?

https://www.irs.gov/forms-pubs/about-form-970