$ ~/openupi$ pwd
/home/<user>/openupi

$ ~/openupi$ cat install-config.yaml
apiVersion: v1
baseDomain: noiro.local
compute:
- hyperthreading: Enabled
  name: worker
  replicas: 0
controlPlane:
  hyperthreading: Enabled
  name: master
  replicas: 3
metadata:
  name: openupi
networking:
  clusterNetwork:
  - cidr: 10.2.0.0/16
    hostPrefix: 23
  networkType: CiscoACI
  serviceNetwork:
  - 172.30.0.0/16
platform:
  none: {}
fips: false
proxy:
  httpsProxy: <http-proxy>
  httpProxy: <https-proxy>
  noProxy: <no-proxy>
publish: External
pullSecret: <RH-account-pull-secret>
sshKey: <host-ssh-key>

# Configuration for ACI Fabric
#
aci_config:
  system_id: openupi                       # Every opflex cluster on the same fabric must have a distict ID
  apic_hosts:                           # List of APIC hosts to connect to for APIC API access
    - <APIC-IP>
  apic_login:
    username: <username>
    password: <password>
  vmm_domain:                     # Kubernetes VMM domain configuration
    encap_type: vxlan             # Encap mode: vxlan or vlan
    mcast_range:                  # Every vxlan VMM on the same fabric must use a distinct range
        start: 225.115.1.1
        end: 225.115.255.255
    nested_inside:
       installer_provisioned_lb_ip: <loadbalancer_ip>    # This IP should match the one configured in the loadbalancer during installation.
  # The following resources must already exist on the APIC,
  # this is a reference to use them
  aep: <AAEP_NAME>            # The attachment profile for ports/VPCs connected to this cluster
  vrf:                         # VRF used to create all subnets used by this Kubernetes cluster
    name: <VRF_NAME>           # This should exist, the provisioning tool does not create it
    tenant: <TENANT>            # This can be tenant for this cluster (system-id) or common
  l3out:                       # L3out to use for this kubernetes cluster (in the VRF above)
    name:<L3OUT_NAME>        # This is used to provision external service IPs/LB
    external_networks:
        <EXTERNAL_EPG_NAME>    # This should also exist, the provisioning tool does not create it
#
# Networks used by Kubernetes
#
net_config:
  node_subnet: 172.253.3.1/24         # Subnet to use for nodes
  pod_subnet: 10.2.0.1/16           # Subnet to use for Kubernetes Pods
  extern_dynamic: 10.3.0.1/16       # Subnet to use for dynamically allocated external services
  extern_static: 10.4.0.1/16        # Subnet to use for statically allocated external services
  node_svc_subnet: 10.5.0.1/16      # Subnet to use for service graph
  kubeapi_vlan: 3                   # The VLAN used by the internal physdom for nodes
  service_vlan: 202                   # The VLAN used for external LoadBalancer services
  infra_vlan: 4093

Customize the sample acc-provision input file shown above as per your requirements. Then install the latest acc-provision package and run the acc-provision as follows:

$ ~/openupi$ pwd
/home/<user>/openupi

$ ~/openupi$ acc-provision -a -c acc_provision_input.yaml -f openshift-4.12-baremetal -u <user> -p <password> -o aci_deployment.yaml -z aci deployment.yaml.tar.gz

This generates a new aci_deployment.yaml.tar.gz file which contains the ACI CNI manifests, and is used later during the OpenShift installation.