Start anew; especially after an attempt has failed. ‘Drawing board’ refers to a working plan such as from an architect or engineer, and after one plan failed, it was time to return and work up a new plan on the board. (Compare to Back to the basics or  Back to square one.)

“We tried to sell colored toilet paper, but no one would buy it, so we went back to the drawing  board and  came up with fragrant toilet paper.”