Frequency capping can be found in the basic tab of the campaign creation / configuration section.
The default value is 1 ad impression every 24 hours but you customize the maximum number of impressions as well as the time frame after which the counter is reset. The time frame is expressed in hours and does not allow for decimals.
To display your ads to the same user as many times as possible you can type 0 as the number of impressions which will set the campaign to uncapped mode.
Remember that frequency capping is global for each unique user across the whole network so a user will not see the same campaign, even if he navigates to other websites / placements, for as long as he is capped.