To manage how crawl limits are allocated to Campaigns in the account, navigate to the Campaigns page in the Settings menu in the upper-right part of the screen.
At the Campaigns page, you can click on the wording (Either a number or (no limit)) under the Crawl Limits column for the campaign you'd like to adjust:
You will get a popup, allowing you to define a new crawl limit, after entering the number click on the tick icon to save.
You may remove a crawl limit by leaving its value blank, if you want to disable crawling for the campaign, use 0 as the crawl limit.
You can also change crawl limits in the campaign by modifying campaign settings.