I have used Post call using this API rest/raven/1.0/import/execution and the body format is below to update the description in Test execution. I am getting a 200 response and also in the test execution it's showing that updated a minute ago but the description doesn't get updated :
{
"testExecutionKey": "DEMO-1206",
"info" : {
"description" : "This execution is automatically created when importing execution results from an external source"
}
}