You can share your private TMs with other users by sending them the private key. In order to do this, click on the arrow of the dropdown menu next to the Import TMX button and select Share resource. You can then enter the email address of the person you wish to share it with inside the text box. If they have an account on Matecat, the private key will be added directly to their translation memory and terminology tab; otherwise they will need to click on the Add a shared resource button and paste the key into the private TM key field and then click on confirm.
Please note that only the job owner can modify the TM settings.
So if you share a TM key associated with an existing job, the translator will see the TM key but will not be able to modify the TM settings of that job.