Let's say you have multiple repos, perhaps something like this.

https://github.com/acme/foo.git
https://github.com/acme/bar.git
https://github.com/acme/hello.git
https://github.com/acme/world.git

And each of these repos can be added to ArgoCD using the same credentials, such as the same username and password.

argocd repo add https://github.com/acme/foo.git   --username john.doe --password itsasecret
argocd repo add https://github.com/acme/bar.git   --username john.doe --password itsasecret
argocd repo add https://github.com/acme/hello.git --username john.doe --password itsasecret
argocd repo add https://github.com/acme/world.git --username john.doe --password itsasecret

Or the same token.

argocd repo add https://github.com/acme/foo.git   --username ' '  --password 'ghp_ggEVZkS0N2mzlGABCK0pO3C123CSmS0oFNeX'
argocd repo add https://github.com/acme/bar.git   --username ' '  --password 'ghp_ggEVZkS0N2mzlGABCK0pO3C123CSmS0oFNeX'
argocd repo add https://github.com/acme/hello.git --username ' '  --password 'ghp_ggEVZkS0N2mzlGABCK0pO3C123CSmS0oFNeX'
argocd repo add https://github.com/acme/world.git --username ' '  --password 'ghp_ggEVZkS0N2mzlGABCK0pO3C123CSmS0oFNeX'

Or the same SSH key.

argocd repo add git@github.com:acme/foo.git   --ssh-private-key-path $HOME/.ssh/argocd
argocd repo add git@github.com:acme/bar.git   --ssh-private-key-path $HOME/.ssh/argocd
argocd repo add git@github.com:acme/hello.git --ssh-private-key-path $HOME/.ssh/argocd
argocd repo add git@github.com:acme/world.git --ssh-private-key-path $HOME/.ssh/argocd

This is a good scenario to add a Credential Template to ArgoCD so that when adding repo's to ArgoCD you don't need to include the username and password or token or SSH key and instead the repo will be added using the Credential Template. The argocd repocreds list command can be used to list the Credential Template that have been added to ArgoCD..

~]$ argocd repocreds list
URL PATTERN                  USERNAME  SSH_CREDS  TLS_CREDS
https://github.com/acme                false      false

Or in the ArgoCD console at Settings > Repositories.