Without having Thunderbird to work with, the instructions would probably be useless to me as well.
If you have registered on their Community, ask if someone could walk you through the steps - I'm sure you would find someone to help you.
That doesn't bode well for an 18 month old machine, but hopefully the replacements will last a lot longer.
In 2011 I bought my younger son and his wife a Toshiba laptop which had the motherboard go down after just two years.
I salvaged it, had the motherboard replaced and upgraded it to Win 10 which is this machine and so far it's going okay, given that it isn't supposed to be Win 10 compatible.