I found the swagger-ui., but the only functionality I can imagine to do this job (I found) was the application patch method (swagger-ui#operation/Patch). But I find no explanation how to do it.
The explanation I found is for the cli tool of argocd (https://argoproj.github.io/argo-cd/user-guide/parameters/) which does not really help me.
The whole point of adopting GitOps is to use Git as a single source of truth.If you want to change your application with ArgoCD you are expected to commit your change to the Git repository watched by ArgoCD.
Changing manually values via REST APIs is against GitOps.