You need to copy the files wsjt.log and wsjt_log.adi from your WSJT-X application folder over to the new JTDX application folder.
This is mentioned in the JTDX documentation.
JTDX uses the same log file name structure as WSJT-X.
The WSJT-X files are located in: C:\Users\<username>\AppData\Local\WSJT-X.
Copy them over to the JTDX folder, and allow them to overwrite the existing files. The JTDX folder is at: C:\Users\<username>\AppData\Local\JTDX