How do I update my HOR with a DD 2058? Does it go through IPPS-A or is it still submitted from through S-1?

From your description, you're not changing your HOR, you're changing your current residence. You can easily do that yourself in IPPS-A*.

A DD Form 2058 is used to change your State of legal residence with DFAS in order to change which state taxes are withheld from your pay.

If that's what you're trying to do, for that and all pay inquires you'd submit a CRM in IPPS-A (IPPS-A Help Center -> Create a case) with the attached documents, description, etc.

CRMs are routed to the lowest level provider group (usually the BN S-1), and they reroute the CRMs they can't address to the appropriate office (in this case, the servicing Army Military Pay Office) who will also follow the same process.
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* The Personal Details Page will show the SM's Picture, Rank, Full Name, and MOS in the Top-left corner of this page. This page should list Two addresses for the SM: Home Address and Mailing Address. The SM should be able to update any Address by hovering over the address box they want to update and clicking that area.

While not providing any guidance on what you need, HOR is static. State of residence is a different matter.

For USAR, the DD2058 is still being processed by the pay team to update a change of residence for tax purposes. Send it to your pay person/team (S1/ARA/RPAC).