Hi,
Thank you for all your help. Below is the version that is shown on LS "LimeSurvey Community Edition Version 6.10.2+250127".

As you can see in the screenshot below. In Picture 1, under the import question, it shows the following message: " Select question file (*.lsq):"
As seen in Picture 2, if I upload an .lss file, I get an error message as " Unknown extension. This can be seen in Picture 3.

I know it is not safe, but I also tried converting the .lss file to the .lsq file, but I got an error message like "The languages of the imported question file must at least include the base language of this survey."

Thanks again for your help.

Best,
Fatima

Not surprising.
You try to import a question; therefore the extension is "lsq" (limesurvey question).

As you were told before you have to import a "lss" (limesurvey  structure).

By the way: There is a third type "lsg" (limesurvey group) that contains an entire group.

When you create a new survey, you will see three options 
"Create"
"Import"
"Copy"

Here you select "import".

Joffm