To access this feature, you will need to go to the Setting's page by clicking your profile photo located at the right side.

When you click on it you'll see Auto Withdrawals option below. You will be able to select from 7, 14, 21, 30, 60 or 90 days to automatically withdraw unanswered pending connection requests. 

When click 'Save' you'll be seeing the notification below's option 'Auto withdrawal interval updated'.

Once selected, the bot will check every session how many pending invites you have, how old they are and will withdraw up to 500 of them at a time if required.