When you get the Affidavit of being single for your fiancée from the Colombian government get it translated into English by a certified translation company.
Then write a short letter to the service center that is handling your K1,case with a copy of the Colombian government affidavit of being single, the certified translation and the NOA1 letter.
In your letter - Briefly apologize for forgetting to submit this affidavit and respectfully request it be added to your K1 visa package.
USCIS can accept the addition, or not, it’s up to the visa officer but go ahead and be proactive with this suggestion.
This should cover the service center adjudication.
Upload the certified affidavit of “being single” at the NVC CEAC stage under other documents include the translation.
Bring the original letter to the visa interview.
Then 2 weeks before the face to face visa interview at the embassy both of you write new letters of intent to get married clearly stating you are both single - and legally able to get married in the USA.
You can get the Colombian government affidavit certifying your fiancé is single at this address in Bogotá Colombia -
Carrera 7 - Calle 32 - numero 17 - Edificio San Martin, Bogotá Colombia