Is there anyway I can enable all tests on Jenkins?

Test Completenor jenkins have a built in way to do this, but a very easy solution can be made with powershell which you should be able to execute via batch command from Jenkins.

Test Complete project files are just xml files that can be manipulated pretty easily. We drive all of our test plans with data from Jira to determine if a test item should or should not be ran.

Something like this should enable all test items in a project if that is what you are defining as a test. 

function enabledAll(){
	[xml]$xml = Get-Content <path to project>
	Write-Host "Enabling all test items in project"
	$testItems = Select-Xml -Xml $xml -XPath ".//testItem[@group='False']"
	foreach($test in $testItems){
		$test.Node.enabled = "True"
	}
}