Looking for the form to reschedule drill assembly?

SPC (Join to see), MSG (Join to see) is correct, typically the servicing RD provides a template for the units. It would look something like: https://www.ozarkwarriors.com/forms/RST-414-2.pdf [don't use that one unless your unit is serviced by the 89th RD]

Your ARA, FLL, PSG should all have a copy of the form available. Remember, only the Commander (or the 1SG if delegated) can approve an RST request. You can submit the form, but w/o the CDR's signature, it is still a request. Some units won't have it signed when you show up for duty and ARAs shouldn't process the payment without the signature.

Don't forget that you still have to submit both the approved RST form and a DA Form 1380 after the duty is performed to get paid.

You get it from your unit.

As others have said, talk to your first line leader. RST forms are organization specific. Make sure you have what you need to back up the excusal and that it doesn't fall on a "mandatory" BTA. Best of luck!