To exercise a warrant grant into a stock grant, head to the Cap Table tab on the left panel. Click Warrants from the top and select the warrant you want to exercise by clicking its Cert. number. Click Cancel Grant from top. In the comments section, you can add a note that the warrant is being cancelled due to exercise.
Once the warrants is cancelled, you can create the corresponding stock grant from the quick create menu (+ icon) on the left panel. In the grant's comments section, add a note to indicate the grant's origins.