There are several ways of updating a TM during, before or after the translation process.
The TM used in the translation process is either automatically updated by receiving new translation units whenever a segment has been translated and closed, or it is manually updated at the end of a translation project or file, when the translator selects the option to send all translation units of the project to the TM.
Another possibility for updating a TM is to import data from a different TM or even from a TM created in another TM system. This is often the case if customers maintain their own TMs and provide parts of them for certain translation projects.
For details on importing TMs, see the course on Creating and Updating TMs.