How do i update awards for arb?

Unless you have access to the system to update the ARB, you are not going to be able to update any ARBs. Also, substantiating documents will be found in iPerms (if the Soldier submitted the docs to S1 for iPerm). If they are not in iPerms, then they need to be brought in by said Soldier(s) then scanned into iPerms. Again, if you do not have access to the system for iPerms and RCMS....and any other system that assists in updating SMs administrative areas, you are not going to be able to assist in that avenue. But to answer the part of what documents you need....you need the signed memo from the unit Commander awarding the Soldier the AFRAM and the ARCAM.

If you are updating a record brief, you should only update based on those supporting documents that are in the soldier's iPERMS.
If you don't know what documents are required to update an award on a record brief, then you really need to sit down with someone in your S1 for at least an hour of training before you just log into RCMS and start editing ERBs.

Without the proper access/training to personnel management systems mentioned already, you will be at a standstill. Any good S-1 should have an SOP on processing awards, source documents needed, etc.

So for starters, you will need at least some of the following:
AR 600-8-22 Ch 4, Para 4-14 thru 4-19

Source documents:
NGB Form 23A Retirement Points Annual Statement (if the Soldier transferred from the National Guard to Reserves)
DA Form 5016 Chronological Statement of Retirement Points(USAR)

DD-214(s) - are a reference point:
You will need to know when they got mobilized and returned from mobilization. There's a part of the regulation that states "The qualifying time for awarding of the ARCAM, served prior to activation/mobilization, will not be lost and will continue to count toward award of the ARCAM once personnel are no longer activated/mobilized". (para 4–18d(3))
Some of the information may overlap because in some instances the servicemember may qualify for an Army Good Conduct Medal(AGCM), and you can't use the AGCM period of service to award an ARCAM for the same period.

Last but not least, orders, mobilization orders activating, and return from mobilization.

This is not an all-encompassing list but the S-1 should have an SOP on this. Also, the award of the ARCAM is on an official memorandum not published orders. The S-1 should have a template readily available.