Regarding importing and exporting via LOTW
First, I assume you have already filled in the configuration and account details mentioned above. Next, I will look for "lotw" within the third-party service.

Click to upload the certificate, and submit the "call sign information" you obtained from the TQSL software. Click the "Save as call sign" or similar button (there are four buttons on that page, try them one by one). This will display a "Save As" interface showing the "callsign.p12" file to be uploaded here. Then complete the upload.
The next step is to wait for the administrator to fix the synchronization issue.
If you want to export logs to LOTW, simply click on "Manual Sync" and it will be fine.