There is no Calibration for the TPA-BNC; there is only a Functional check. If the probe your using it with works, talks to the scope, and meets specifications, the TPA-BNC is working.
Our service department does offer this Functional check if needed, at a cost of about $265.
To set up a repair RMA (model and serial number)
call 1-800-833-9200 opt 2. Or 1- 800-438-8165
Or send an email to rmarequest@tektronix.com
Or https://www.tek.com/en/service-quote
Or https://www.tek.com/en/services/repair/mytek_rma_request