Your question seems incomplete. However, to access a namedValue within an APIM policy you refer to it like:
<some-xml>{{Test-namedValues}}</some-xml>
Where {{Test-namedValues}}
is the name of the namedValue which has it's own value assigned to it, or via Key Vault.
You can read more here: https://learn.microsoft.com/en-us/azure/api-management/api-management-howto-properties?tabs=azure-portal
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