The Monash University is the go-to site for good advice.
I didn't use any apps. I don't access the internet via my phone, but a laptop and apps for smartphones won't load for me. No issue. I'm happy about that. So my way through the 8 week Low Fodmap trial, and the re-introduction phase was done with good old fashioned pen and paper, a food diary, symptom diary, a graph, etc!
I must say, trying the Low Fodmap diet was definitely worth it. Did it solve my IBS issues? No.
I found that some low Fodmap foods didn't agree with me from day one. Some high Fodmaps did. To cut a long story short it was worth trying, but my IBS didn't behave logically at all in response to it, Whether low Fodmap or not, my IBS just kept on doing its own thing, so really the results weren't as clear as I'd hoped for.
But nevertheless I stuck to Low Fodmap for the full 8 weeks and even went gluten free (even though gluten causes me no problems.)
However, the diet worked beautifully for a friend of mine who also had IBS.
We are all so different, with umpteen triggers for our symptoms, and umpteen ways to cope with that and even hopefully -heal.
It was a LOT of research because I also added a deep study of nutrition. I had to, as no dietician was available (I did all this during the UK "Lockdown" in 2020 when it was difficult to get a doctor's appointment, never mind a dietician on the NHS!
So I pulled out all the stops, and did the work myself. I also took vitamin and mineral supplements at RDA dosage to help me through so there would be no basic deficiencies.
Your very best plan would be to see if you can get a dietician to help you navigate the Fodmap diet and re-introduction. It would be much more helpful that way if possible.