If you haven't yet uploaded the offer to Cake you will need to do so first by following the steps in this article -> Uploading accepted stock option grants. When the offer has been uploaded and granted you can record the cancellation by following the instructions in one of the two methods below -
Method 1
Go to Equity Plans then Options/Stock Options in you main menu
Click 'View Pool'
Find the relevant offer in the list and click on the 'Lapse' icon on the right hand side
In the pop up, enter the date of lapsing. All options with a vesting event prior to the lapse date will automatically vest, all the remaining unvested options will lapse.
If you wish to accelerate the vesting you can do so by ticking the box for accelerated vesting. You will then have the option to manually type in the number of options to accelerate.
Click 'Lapse' and you are all done!
Method 2
Go to Captable then Option Holders in you main menu
Click 'More' and select 'Lapse Options' in the drop down box as shown in the image below.
Select the relevant option holder and offer
Proceed to step number 4 in Method 1