Hi @Sandie
If you are seeing the "Let's get Started" screen and either get stuck at this stage or the next screen page then it looks like you have done a full factory reset on the NOW Stick.
If the NOW voice Smart remote has developed a fault and can't be fixed then the Roku remote App for mobile won't be of any use (you need a physical NOW smart voice remote to setup the Stick again from factory reset before you can use the Roku Remote App on your mobile).
Only other things you could try is a different wifi channel and wifi band on your Router (use the lower wifi channels) and after inserting fresh batteries try the NOW remote close to the Stick at the back of the TV, you could also try a second TV in the home if you have one with the Stick.
My NOW smart voice remote controller gave up the ghost a few months back and everything I tried didn't work for me (though I am lucky where I have plenty of other NOW devices such has Roku's or an Amazon Fire Stick to fall back on).
