How to add remove clusters to existing namespace from tctl

Hi i have a namespace, which i made global using tctl --ns up --pn

now i want to add an additional cluster to this namespace and i tried

tctl --ns up --cluster clusterA,clusterB

but it id not not work,

how cal i pass cluster info in --cluster?

ok realized that tctl --ns somenamespace up --cluster clusterA clusterB clusterC