Warp Group is a functionality of Designer – via menu “Layer → Warp Group”, or an icon at the bottom of the Layers Panel.
Just type warp group into Designer’s Help to get more information.
You might be lucky finding a tutorial but this functionality hasn’t been in Designer for very long so there may not be lots to choose from.
There’s probably an official video about it https://affinity.serif.com/en-gb/learn/ but I don’t know if it will show you exactly what you want to do.
Here's a link to a tube vid where the guy uses Photo to do what you want. I have his site bookmarked. He has a lot of useful info for a guy like me who knows nothing.
https://www.youtube.com/watch?v=5VaF5rU0aXg