hi my dear friends :
what does select all and unselect all after search a satellite in lost channels box mean?
my another Q is what are lost channels ?

thanks in advance

Channels that are in the list, but were not detected on the scan, can be marked, to get deleted.
This makes sense for stations, that have been closed, but it's not helpful for stations, that have just been inactive at scan time, but would return later on.
That's why you can select to allow deleting or not.

BTW, all your recent questions belong to the same issue, more or less.
In such a case, it does not really help, to open three new threads.