There are two small bias trim pots next to each of the two banks of tubes; however, do not touch them unless you have a voltmeter and have the instructions from Sonic Frontiers that they will fax to you. If you order the matched sets from Sonic Frontiers, they will include a drawing of these trim pots and where you should set them for the tubes you are getting from them.
However, I understand that it is not critical, and you can just leave them alone. If you get tubes from another source, I would not touch them, unless you do the voltmeter procedures outlined by Sonic Frontiers.
When I asked Kevin of Upscale Audio, he said he has never touched them or adjusted them and the replacement tubes he has sold have worked fine.