The import channels function never made it into v5 unfortunately. If you're adding a tuner that is the same type as one you already have, then you will be prompted to add the channels from that other similar tuner, but that's the only time you get any kind of "import" function.
With 20+ tuner types an import is very difficult to document and implement, and I expect troubles if users try to create them manually. If the tuner is new or types aren't the same you will need to scan and merge. If the scan scan is not finding the channel you want then support logs aren't required and safer then importing.