How to bundle intermediate certs into one file

I manage an apache web server for a government site. The SSL cert will expired in a few weeks so they sent me a zip file with 3 intermediate certs and the ssl certificate (I have the private key from the csr generator and the crt file provided by gov’t). I need to bundle the intermediate certs into one file for apache2.

Here are the 3 intermediate certs they sent me

Jan  1  2004 AAACertificateServices.crt
Nov  2  2018 SectigoRSADomainValidationSecureServerCA.crt
Mar 12  2019 USERTrustRSAAAACA.crt

In what order should I bundled the 3 certs because from reading from other links, the order does matter if the root is provided. Which one is the root?

I used an online ssl validator for the the 3 certs

AAACertificateServices.crt

Common Name: AAA Certificate Services
Organization: Comodo CA Limited
Locality: Salford
State: Greater Manchester
Country: GB
Valid From: December 31, 2003
Valid To: December 31, 2028
Issuer: AAA Certificate Services, Comodo CA Limited
Serial Number: 1 (0x1)

SectigoRSADomainValidationSecureServerCA.crt

Common Name: Sectigo RSA Domain Validation Secure Server CA
Organization: Sectigo Limited
Locality: Salford
State: Greater Manchester
Country: GB
Valid From: November 1, 2018
Valid To: December 31, 2030
Issuer: USERTrust RSA Certification Authority, The USERTRUST Network Write review of Sectigo
Serial Number: 7d5b5126b476ba11db74160bbc530da7

USERTrustRSAAAACA.crt

Common Name: USERTrust RSA Certification Authority
Organization: The USERTRUST Network
Locality: Jersey City
State: New Jersey
Country: US
Valid From: March 11, 2019
Valid To: December 31, 2028
Issuer: AAA Certificate Services, Comodo CA Limited Write review of Sectigo
Serial Number: 3972443af922b751d7d36c10dd313595

This has been a gray area for me since I’ve been using LetEncrypt and they automatically bundle the intermediate certs on to one file.