How do i remark a dataset as "removed" ? The result is that this dataset is no longer appear on UI

you can set its status to 'removed' by adding the status aspect to its snapshot.aspects array

{
  "com.linkedin.common.Status": {
    "removed": true
  }
}

Do you mean that i should ingest this dataset again in a json file adding the status aspect above ?

you dont have to ingest the original json, just attach a new aspect to the dataset. something like this (adjust the urn to your dataset) would do

{
  "snapshot": {
    "urn": "urn:li:dataset:(urn:li:dataPlatform:dataset,PROD)",
    "aspects": [      
      {
        "com.linkedin.common.Status": {
          "removed": True
        }
      },
    ]
  }
}

+1!