Currently, task ownership can be reassigned on wherever you can locate the task (via the deal, contact record or if it is associated with a workflow). Though the function of actually assigning the new task owner is still a manual process, where you would select the dropdown near the name under “Assigned to” and from there the task would be assigned to who is selected.
I found these community posts Task-based workflows, and Reassigning tasks when ownership changes that others have posted to try and generate this to become a feature (i went ahead and gave them both upvotes for you! and think it would help to generate more traffic if you liked as well as added you own comment) I also located this document Assign ownership of records that provides more detail on assigning ownership of records.
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