You can assign a Salesforce task to another Salesforce user by following these steps:
Go to Tasks Overdue / Tasks Upcoming on Dashboard.
Tap on the plus ( + ) button at the top on the right.
3. Choose the Salesforce user you want to assign the task to.
4. Choose the Salesforce account / contact / lead for the task OR create a new one.
5. Choose the type of Task.
6. Choose the due data of the task
7. Add task description by typing or using Speech-to-text feature (Optional).
8. Complete with right arrow button.