Changing index size of _audit index on a cluster

I have a cluster set up with 1 index master, and 2 index peers. I would like to change the size of the _audit index from 500G to 400G. How can I go about changing these? On my index master, in the inputs.conf file that gets pushed out, there is no _audit index since these are created from splunk setup. I cannot go to each peer and change them manually, b/c the peers are part of a cluster. Thanks!