While there is no TM editor integrated in Smartcat, there are some very good options that are in some ways more powerful than the TM editors provided by other CAT tools:
You can export the TM as an Excel file, edit it externally and re-import it back to Smartcat. You can use all the editing features of Excel to make the changes that you need.
For people that are more tech savvy, they can also export the TM as TMX (with our tags), open it in a text editor like Notepad++ or Sublime Text and perform complex search and replace operations. Even across multiple files if needed. The TM editors included with other CAT tools cannot usually do this.