How to read list of key:values returned by !GetAtt in cloudformation for AWS Network Firewall

I am trying to access 3 network firewall endpoints that gets created in 3 subnets in different AZs to be added to route tables:

Logical name of network firewall is "NetworkFirewall"

!GetAtt NetworkFirewall.EndpointIds.${AWS::Region}a
!GetAtt NetworkFirewall.EndpointIds.${AWS::Region}b
!GetAtt NetworkFirewall.EndpointIds.${AWS::Region}c

As specified in AWS docs:

Fn::GetAtt
The Fn::GetAtt intrinsic function returns a value for a specified attribute of this type. The following are the available attributes and sample return values.

For more information about using the Fn::GetAtt intrinsic function, see Fn::GetAtt.

EndpointIds
The unique IDs of the firewall endpoints for all of the subnets that you attached to the firewall. The subnets are not listed in any particular order. For example: ["us-west-2c:vpce-111122223333", "us-west-2a:vpce-987654321098", "us-west-2b:vpce-012345678901"].

But this way:
!GetAtt NetworkFirewall.EndpointIds.${AWS::Region}a
of accessing endpoints, seems to be not working.

So I tried
!GetAtt NetworkFirewall.EndpointIds, which would return list of 3 key:value pairs, from which I need to extract networkfirewall endpoints for each AZ's and use them in related route table, using Cloudformation

Any tips will be helpfull

Start with the AWS CloudFormation Fn::GetAtt documentation and the AWS Network Firewall EndpointIds attribute described in the issue. Reproduce the reported access pattern and determine how the returned endpoint values can be associated with the three route tables; done means the issue documents or demonstrates a working approach.

Written by the indexing model from the issue text.