Retroactively adding performance tickets to constituent records

My organization is still new to Tessitura, and we are hoping to figure out how to keep records of registration/attendance on performances that were ticketed externally. The way that our Tessitura onboarding team handled this for old performances from before our conversion was by adding tickets to the Tickets page of each attending constituent record, as shown. 

Most of our performances are now ticketed internally through Tessitura's ticket orders system, but we still have some for which constituents register externally, e.g. through Zoom. These performances are created in Tessitura as well and given performance codes, but we would need a method of manually bringing the registration information into Tessitura so it exists on the performance record and the constituent records of attendees, not dissimilar to what Onboarding did for us during the conversion process. Is this something that we could also do ourselves?