I need to pass the ArgoCD token as a cookies header to the delete API.

For

<=v1.2

Then pass using the HTTP SetCookie header, prefixing with argocd.token:

$ curl $ARGOCD_SERVER/api/v1/applications --cookie "argocd.token=$ARGOCD_TOKEN" 
{"metadata":{"selfLink":"/apis/argoproj.io/v1alpha1/namespaces/argocd/applications","resourceVersion":"37755"},"items":...}

v1.3

Then pass using the HTTP Authorization header, prefixing with Bearer:

$ curl $ARGOCD_SERVER/api/v1/applications -H "Authorization: Bearer $ARGOCD_TOKEN" 
{"metadata":{"selfLink":"/apis/argoproj.io/v1alpha1/namespaces/argocd/applications","resourceVersion":"37755"},"items":...}

https://argo-cd.readthedocs.io/en/stable/developer-guide/api-docs/#authorization

and finally my function is able to delete apps from the ArgoCD

async function deleteApp(AppName){
    let url = 'https://argocd.exampple.com/api/v1/applications/'+AppName
    let res = await fetch(url, {
        headers: {
            Cookie: 'argocd.token=' + process.env.ARGOCD_AUTH_TOKEN 
        },
        method: 'DELETE'
    })
    let body = await res.json()
    return body
}