On receipt of the engineer’s report filed under section 357.10, the board of supervisors shall give notice in the manner provided in section 357.4 of a hearing on the engineer’s tentative design and dummy plat. On the day set, or within ten days thereafter, the board of supervisors shall approve or disapprove the engineer’s plan and proposed assessment. If it shall appear advisable, the board of supervisors may make changes in the design and assessment, as they appear on the dummy plat.