Strange request. In using POL, is it possible for a team member to update their tasks in Planner? I'm assuming they would still need to pay for a Plan 1 licence.
There is no way out of the box to push tasks from a project in Project Online to a Planner plan or Planner tasks back to Project Online. There are 3rd party solutions that do this I believe but I've never used any of these. The only option of out the box is to create a link from a task in Project Desktop to a Planner plan but there is no sync of data: https://pwmather.wordpress.com/2017/08/29/link-projectonline-tasks-to-planner-microsoft365-ppm-pmot-...
