Section 600 of the Act can be found here - https://www.congress.gov/bill/115th-cong...14E7041BE46C53B
What this did was modify Sect. 3937 (b)(1) of the SCRA which you can find at this link, with the Editor's Note as to the effective date or August 13, 2018, which was when it was signed into law. https://www.bankersonline.com/regulations/scra-527
Previously this Section required the servicemember to provide a copy of their orders to obtain the 6 percent rate. Many, if not most banks would accept other proof such as the DMDC database verification often used for SCRA and MLA purposes. The revision provides a safe harbor for using the database which could be advantageous if a request is denied. Alternatively the orders may still be required and a letter from the servicemembers commanding officer is also acceptable.
With the exception of a bank having a safe harbor, which would come into play if a servicemember was denied protections, much of what this amendment does was being practiced anyway perhaps with the exception of accepting a commanders letter which is now an official alternative to orders. I see this as a low-risk event or one that if it presents itself, may be easily verified.
Just as you could not find a specific effective date, nor could I. Many Titles and Subtitles and Sections contain effective dates but Subtitle J and Section 600 does not. Some dates do refer to January 1, 2019, January 1, 2020, December 31, 2018 and effective when signed, as examples. Absent a stated effective the date, the a law becomes effective the date the Act is signed into law, and in this case that is August 13, 2018.