It's hardly high-tech rocket science to fit/refit a jack-plug on a headset.
Any retail electronics specialist in Audio/Pop-Group Amplification/Radio&TV etc. should have an engineer able to do this. even the local tv/radio repairer.
Wether the repair can be documented (or needs to be!) to Certified standards is another issue.
If it were my own, I'd do my own repair and keep schtum...if it belongs to someone else,-it's their problem (fair wear and tear.)