It's hard to be sure without seeing your data, but you could try try the following rex command
... | rex field=_raw "Bearer\s(?<bearer_token>[^\s]+) "| table bearer_token
Modify the regex as required based on your data. https://regex101.com/ is a good place to test regex strings.
See http://docs.splunk.com/Documentation/Splunk/6.3.3/SearchReference/Rex
Are you trying to search for a specific token or extract the value of bearer ?
Extract the value of the tokens after the word Bearer