Use the following script to clear the build history from jenkins. Goto Manage Jenkins > Script Console and type the following script
// change this variable to match the name of the job whose builds you want to delete
def jobName = "Your Job Name"
def job = Jenkins.instance.getItem(jobName)
job.getBuilds().each { it.delete() }
// uncomment these lines to reset the build number to 1:
//job.nextBuildNumber = 1
//job.save()