TurboTax does have an entry spot for that specific credit.   Page through the Alabama state credits until you come to the screen titled Let's Check for More Alabama Credits.  The next to last line item is for the AL Investment Credit.  If you click Start or Update there, you can enter all the information and TurboTax will complete Part P.    There is a screenshot of Schedule OC, Part P below.   The amending instructions are linked here.

Thank you Dawn.  Unfortunately, I cannot figure out how to get to the screen you show in your screenshot. For reference, I am using TurboTax Deluxe online version.  I've tried doing this through both the "Guide Me" and the "I'll choose what I work on".  In either case, I never see the screen that says "Let's Check for More Alabama Credits."  Instead, I get to the screen below.  And then, when I check on "Taxes and Credits",  I get a series of specific questions, but none about the Investment Credit (one example included below.  So, I'm struggling to get to the screen you show below.  How do I get to that point?  Thank you!

Click on Update next to Taxes and Credits from your image above, and slowly click through the screens.   The order of screens you will see is:

1. Credit for Tax Paid to another state
2. AL Adoption
3. Non-failing schools
4. Donations
5. Small Town Docs
6. Rehab
7. Neighborhood
8. Dual Enrollment
9. Renewal Act - Carryover
10. Storm Shelter
11. VERT - volunteer emergency responders
12. The next screen is the screen you want.   Lets Check for More Alabama Credits - scroll down to the next to last line item.... 

Thank you again Dawn.

I did as you suggested, and the order I see is:

1. Credit for Tax Paid to another state
2. AL Adoption
3. Non-failing schools
4. Donations
5. Small Town Docs
6. Rehab
7. Neighborhood
8. Dual Enrollment
9. Renewal Act - Carryover
10. Storm Shelter
11. VERT - volunteer emergency responders

However, when I click "Continue" from the "VERT" page, it just takes me back to the page I started from "You've Finished Your Alabama Return".  For some reason, I do not get the "Lets Check for More Alabama Credits" page after VERT.  At this point, I'll probably just fill out my Amended return by hand.  Thank you for your help.

Did this ever get resolved? I am trying to fill out my 2024 return, and I received a letter from the Alabama Department of Revenue saying I have an investment credit.  I have tried everything to figure out how to add this to my Alabama return on Intuit TurboTax Premium.  I have spent hours chatting with your help service, and they have had me walk through every screen multiple times. Can someone please tell me how to complete a Schedule OC Part P and add this credit? I feel like it shouldn't be this hard.

I only get the screen Let's Check for More Alabama Credits, with the Alabama Annual Investment Tax Credit listed if I have entered a business on the federal side of the program. 

If you do have a business reported, I'd suggest deleting the existing Alabama return and starting a new one.