Thanks for the information... The PTZ is a H5 and the only place I can find firmware is off the Hikvision website (it's on the International website for the specific PTZ model).
The firmware file is IPDHG_H5_L1_EN_STD_5.5.27_200109 so the firmware files for the 'normal' T2 PTZ's don't work. From a naming convention they don't have the 'IPDHG' and 'L1' in the file name (e.g. the firmware files are IPD_H5_EN_STD_5.5.27_200109).
The release notes for version 5.5.40_200518 suggest that there is a firmware version (e.g. file name is IPDHG_H5_L1_EN_STD_5.5.40_200518) however I can't find it, hence I wanted to check ftp:/ftp.hikvision.com. Painfully the ftp site prompts for a username & password.