Change Assigned To of the task

Question

Hello All,

I have a workflow in which I am assigning a task to a particular SharePoint group [Not to default "Assignedto" field of Task list, I am taking the group in a custom field and am able update the group name in Task list.

I have an InfoPath where I have fetched the list of users in SharePoint Group. I am able to see the user while am debugging the VSTA.

My problem :

I want to assign the task to the user selected in the dropdown. I am stuck at this point, how to do it? Should I try to get the workflow properties in VSTA and update the assignedTo or should I directly update the task list and use the on task changed activity in workflow. I am confused and am unable to do both the options.

Please help.